RAZ-1 was the Navy designation for a group of equipment
consisting of a four tube longwave TRF receiver with regenerative
detector, a matching one tube preselector and a one tube AC power supply
- all built for shipboard use. The Navy number for the receiver is
CRM-46092 but it was also known as the AR-8503 in commercial
applications. The AR-8503 was in use as early as 1938, mainly in
commercial shipboard radio rooms. The receiver circuit uses one RF
amplifier, a regenerative detector and two stages of AF amplification.
The one tube preselector is Navy number CRM-50092 or commercial number
AR-8503-P and the AC power supply is Navy number CRM-20096 or commercial
number RM-6. Tuning is from 15 KC to 600 KC in four bands. The
Preselector was used to reduce regenerative signal radiation to the
antenna in addition to increasing sensitivity and selectivity. The
National Type "N" dials are 0-100 scaled with 180 deg. rotation and a
calibration chart is included in the manual . The RAZ-1 could be
operated from batteries if necessary. The receiver and preselector
panels are beautiful machine-textured aluminum with a matte-chromium
finish. The receiver case is copper-plated steel under the gray wrinkle
finish and uses "shock-mount" feet that were screwed to the operating
table, (the pre-selector and power supply were normally screwed directly
to the operating table.) The Navy contract is dated December 2, 1941 -
just five days before the attack on Pearl Harbor. The RAZ-1 equipment
shown are all assigned identical serial numbers - SN:65. Performance of
this operational RAZ-1 is incredible with an ability to extract weak
signals out of the noise that is impressive. NBDs from all around North
America, LW BC stations and Navy VLF RTTY stations from around the world
are easily received. Output is to a set of Western Electric 509W
earphones as recommended in the manual.(See our "Vintage Longwave Receivers" webpage for an in
depth article about this receiver.)

Radio
Corporation of America - DZ-2

RCA built the earliest
versions of this radio
direction finding receiver for the Navy for use in search and
navigation. The DZ-2 dates from 1939 though there were additional
contracts built by other companies during WWII. Using 8 tubes in a superhet circuit and tuning
from 15 to 70 kc and from 100 to 1750 kc, the DZ-2 used a rotatable dual
loop antenna and a fixed vertical antenna (usually a "T" wire from the
cockpit to the tail) to determine "true" direction (called Uni-lateral
Reception/Sense.) Non-directional and Bi-directional options were also
provided. The dual loop antenna was mounted in an aerodynamic housing on
the exterior of the fuselage and the remote drive control provided a
readout of the loop's relative position for the radio operator. The DZ-2
also featured a BFO and Audio Filters. The receiver uses a cushioned
shock mount. Power provided by the aircraft battery buss and an external dynamotor
for B+ requirments.

Designed for the Navy
by RCA in 1935, the RAK and RAL receivers were intended to replace the
Sylvania-built RAG and RAH receivers designed in 1933. The RAK/RAL cover
the same frequencies as the RAG/RAH and are about the same approximate
size. Although the Navy had RCA design superhets for both LW and HF (the
RAA and RAB from 1931) there seemed to be a reluctance to use the
superhet on LW and the Navy receivers that followed were all TRF with
Regenerative Detectors until the late-thirties. The RAK and RAL were used in various shipboard
applications (also submarine) up through WWII. The two receivers were
ruggedly built and reliable in their design simplicity. The RAK is a six
tube TRF receiver with regenerative detector that covers 15 kc up to 600
kc in six tuning ranges. The RAL is also a six tube TRF receiver with
regenerative detector but covers 300 kc up to 23 mc in nine tuning
ranges. Tube line up is the same for both sets with four 6D6 tubes and
two type 41 tubes (earlier versions of the RAK and RAL used earlier
version tubes.) Both receivers use a dual dial readout (0/00 to
10/00) that must be correlated to a graph in the manual for tuned
frequency. Each receiver has its own separate power supply, the CRV[CND]-20131, which provides power through a ten foot long cable that
connects to a terminal strip inside the receiver. The power supply uses
a 5Z3 rectifier, an 874 regulator tube and an optional 876 ballast tube
that was supposed to be used when the AC line voltage was subject to
fluctuations (supposedly that would cause instability in the RAL
receiver at higher frequencies.) The AC supplied on ships is any but
stable and fluctuations occur with just about any switched load on the
line. Meters on each receiver monitor the
tube heater voltage (right) and the audio output (left.) The RAK
receivers were intended for CW or MCW reception only as a low pass
filter is permanently connected in the circuit to limit the upper audio
response to about 1200 hz. The RAL has the option of allowing the low
pass filter to be switched out of the circuit (switch in "BROAD"
position) and can therefore can be used to receive voice transmissions
along with CW and MCW signals. An elaborate audio AVC system is employed
in both receivers that was a common RCA circuit that performed as an
"output limiter" to cope with atmospheric noise, static, lightning
bursts and to limit overloading from strong signals. An audio bandpass filter system is also
employed in each receiver that allows the operator to select various
audio frequency ranges via a front panel switch. The audio output Z is
600 ohms and is intended to drive earphones (but it will drive a 600 ohm
Z speaker quite well.) The RAL and the RAK receivers were designed to
work together through a separate control box (CRV[CND]-23073) that
allowed the operator to monitor two frequencies simultaneously (each
receiver tuned to different frequencies with the audio from each
combined) and also to control power to each receiver.

The RAK and RAL
receivers are surprisingly good performers and interesting to operate.
The RAK is a first class longwave receiver and can easily pick up NDBs
from all over North America, WWVB or JJY (Japan's LF WWVB equivalent at
40KC) , along with LW BC stations and any of the VLF Navy RTTY stations
worldwide. The RAL is also an excellent TRF receiver that will function
quite well on the HF ham bands, even copying SSB stations with minimal
drift (since there is no LO or BFO to worry about.) SW BC and AM BC can
also be received with audio quality that is somewhat restricted but
acceptable. The RAK-7 and RAL-7 pair shown in the photo are from 1945
and, like most of the late-version RAK/RAL receivers, they were manufactured by Andrea Radio
Corporation. Use of [ND] in Navy designation indicates Andrea
manufacture and [RV] indicates RCA-Victor. There was also a RAK-8 and
RAL-8 produced with Magnavox as the contractor. (See our "Vintage
Longwave Receivers" webpage for an in depth article about these
receivers.)

RBA,
RBB & RBC Series

Considered by many military radio collectors to be
the ultimate in WWII receiver design, the RBA, RBB and RBC receivers
were "cost-no-object" in design and construction. The resulting
performance was so good that these incredible receivers were still
in-use by the USN two decades after WWII ended. Today, many vintage
military radio amateurs use either the RBB or RBC as their station
receiver while long wave enthusiasts consider the RBA the best vintage
low-frequency receiver available.

RBA-1
CFT-46154

Federal
Telephone & Radio Corporation (for RCA) - RBA Series

In the late thirties, it was becoming apparent that a
replacement receiver was necessary for the aging RAA series of superhet longwave
receivers that were initially designed in 1931. Also, the Navy was still
using the RAG (1933) and the RAK (1935) LF receivers in some
installations. RCA's and the Navy's new design was going to blend the advantages of the TRF
designs of the RAK with the TRF and non-regenerative detector with
tracking BFO of the RAG. For shipboard operation an effort to keep the
radiation on the antenna to a very low level that prevented enemy DF of
the receiver location was necessary. Additionally, the low-level of radiation
allowed the receiver to operate in the presence of other receiving and
transmitting equipment and radar without interference. In order to allow
demodulation of CW signals a "tracking" beat frequency oscillator (BFO)
like that used in the RAG
was incorporated into the design. Since the new receiver was not a superheterodyne, the BFO had to track the tuned frequency, providing a
1kc heterodyne which allowed CW to be readily copied. There were a
couple of reasons for not designing the new LF receiver as a
superheterodyne. First was to allow complete coverage of the tuning
range of 15kc to 600kc. The 1931 solution to this problem had been the
expensive RAA receiver that used four different IFs and BFOs to allow
complete LF coverage. The second was that the conversion process in a
superheterodyne can create a lot of internal noise in the receiver - a
problem when operating in an already noisy slice of the spectrum.

Federal Telephone & Radio Corporation had years of
experience in building shipboard equipment for Mackay Radio and they
were selected as the contractor to build the RBA receivers for RCA.
Federal T & R Corp. was owned
by ITT and had grown out of the old Federal Telegraph Company
that was originally located in Palo Alto, California. FTC's
chief engineer was Frederick Kolster, sometimes credited
inventor of the directional loop antenna. Lee DeForest was
associated with the company at one time. During the
mid-twenties, FTC built consumer radios under the "Kolster"
brand name. Mackay Radio & Telegraph Company had close ties to
FTC and all early Mackay maritime radio equipment was built by
FTC. When Mackay was purchased by ITT in 1928, it was not very
long before FTC also was added to the growing list of companies
owned or controlled by ITT. The purchase took place around 1931
and at this time FTC moved to New Jersey. In New Jersey, FTC
continued to build maritime radio equipment, usually for Mackay
Radio. Around 1940, Federal Telegraph Company's name was changed
to Federal Telephone & Radio Corporation.

At $3000 each, the new RBA receiver was certainly
expensive and a look inside the receiver reveals an incredible level of
electro-mechanical design and construction. The tuning ranges from 15kc
up to 600kc in four bands. The illuminated dial readout is direct in
kilocycles along with a two-dial logging scale. The mechanics of the
design allow for super-smooth operation of the tuning system. The Gain
adjustment controls the sensitivity of the receiver and a gear-driven
auxiliary gain control operates from the tuning dial and provides
constant gain levels across the tuning range. Two meters are provided,
one to monitor Output Level in db and one to monitor the B+ voltage. An
Output Limiter is provided for noisy conditions or unexpected strong
local signals with the Output Level adjustment setting the output
limiter's maximum level. Two levels of selectivity are provided, Broad
selectivity is limited to about a 1300kc audio roll-off via an internal
LP filter and the Sharp position is provided by a 1kc bandpass filter
for CW in noisy conditions or in cases of interference. Audio output is
600 ohms Z and is intended for earphones although the RBA will drive a
matched loud speaker if necessary.

photo right: CFT-46300,
RBA-6 from 1945

photo above: RBA-1, CFT-46154, Modified by Field
Changes installed that removed the toggle switches for CW OSC
and Selectivity and replaced them with two position rotary
switches. Front panel repaint but cabinet is still black wrinkle
on this receiver.

The separate power supply, CRV-20130, provides
the filament voltage and B+ requirements via an armored cable
with heavy-duty connectors. The power supply will easily operate
two receivers for emergency conditions and two separate
connectors are provided. This is the same power supply used for
the RBB and RBC
receivers (although the 17vac required for the RBB and RBC is not used
by the RBA receiver.) The power supply has a cold-cathode regulator tube (OC3) and
a HV rectifier (5U4.) The RBA uses eight tubes, three 6SK7 RF
amplifiers, one 6J5 Triode Detector, one 6SK7 BFO, two 6SJ7 AF
amplifiers and one 6K6 AF Output.

The table top versions of the RBA receiver are
identified as C(FT)-46154 or 46154-A (FT identifies Federal
Tele.&Radio Corp. as the contractor) but rack mount versions use
CFT-46300 as the receiver identification. Shown in the header
photo is the CFT-46154 RBA-1 from 1943. All versions of the RBA's receiver circuitry are identical. RBA-1 to RBA-5 were
black wrinkle finish but the RBA-6 was smooth gray paint as
supplied to the USN. Many early RBA receivers were later repainted by
the USN so it isn't uncommon to find early versions that were
originally black wrinkle finish but are now smooth gray paint.

The RBA receivers are impressive performers with
incredible sensitivity, direct
dial read-out with illumination and a tracking BFO rather than
regenerative-autodyne detector. The tracking BFO actually works
quite well for finding the carrier on NBDs. The dial accuracy is
excellent and allows tuning NDBs by frequency rather than
constantly referring to charts or graphs. The LP filter does
limit the audio frequency response on BC stations but not to the
point where the voice is incomprehensible. The OL works quite
well at limiting the maximum output and not distorting the
signal (unless advanced too far.) The RBA is a first-class longwave receiver capable of
receiving any of the LW signals found below 500kc. (See our
"Vintage Longwave Receivers" webpage for an in-depth
article about the RBA and how to achieve the best performance
from these incredible receivers.)

Radio Corporation of America
RBB (CRV-46147) and RBC (CRV-46148)

In 1939, the Department of the Navy contracted with RCA
to build the ultimate military communications receiver. The design was
to replace the aging RAB superhet receivers with new receivers
of the same rugged construction but with much more modern design and performance
capabilities. RCA utilized input from engineers from 17 other companies
during the design phase of the new receivers. By 1940, the RBA, RBB and
RBC were ready for production. The RBA was a TRF LW receiver that
matched the RBB and RBC in size and power requirements (description above.) The RBB and RBC were double preselection superheterodynes using 15 tubes plus a 991 neon bulb
voltage limiter in the antenna input, a 6-8B Ballast tube for the Local
Oscillator heater and the separate CRV-20130 power supply also used two
tubes, a 5U4 rectifier and a VT-105 (0C3) regulator - 19 tubes in all. The RBB
receiver covers 500kc up to 4.0mc in four bands and the RBC covers 4.0mc
to 27.0mc, also in four bands. The Local Oscillator's filament is
operated from a 17vac tap on the power transformer through the 6-8B
ballast tube also the LO's plate is operated from the regulated 105vdc
supply. This design effort allowed the RBB/RBC receivers to exhibit very
little drift. >>>

photo above: This photo shows the McMurdo Station
in Antarctica in 1956. The RBA, RBB and RBC were still in active use by
the USN at this time over ten years after WWII ended.
photo from: https://photolibrary.usap.gov/Tools/DrawImage.aspx?filename=RADIOSHACKB1956.JPG

>>> Three IF amplifier stages were used along with a
three step selectivity control, a noise limiter control and a switchable
audio bandpass filter. Since the AVC could not be on when receiving CW
signals, an Output Limiter circuit could be switched in (CW-OL) to keep
static bursts or unexpected strong signals from overloading the receiver
or the operator's ears. An adjustable squelch control called a
"Silencer" was also included. The construction of the receivers were as
much as possible alike allowing many of the same parts to be used for
each model. There are some tube and component differences in the
preselector section of the RBB/RBC but the IF/AF section is identical
for either receiver. Three panel meters provided monitoring of Signal
Level in db, Audio Output in db and B+ in volts dc. The audio output was
designed for 600 ohm Z earphones and up to 20 pairs could be connected
in parallel, (who knows why but that's what the manual indicates - 30Z
ohm load.) Some
of the later RBB/RBC receivers will have an additional 6AB7 tube
installed along with a SO239 connector on the back of the receiver. This
was an amplified IF output source generally used for a panadaptor. An
internally mounted switch allowed the operator to select this IF
amplifier output function if desired. The entire cabinet was mounted to
the operating table by four shock mounts.

Unlike many earlier USN receivers, the RBB/RBC had accurate
direct frequency readout dials that were illuminated and there was also
a "power on" pilot lamp. The CRV-20130 power supply was connected via a
heavy-duty, "armored" (metal braided) cable with huge nine-pin MIL connectors. Although the
CRV-20130 power supply does provide two connectors to allow operation of
two receivers with only one power supply, this was considered as
"emergency only" operation. When operating two receivers from one power
supply, both receivers will be "ON" regardless of which receiver's power
switch is activated. The load of both receivers on one power supply
drops the B+ voltage and the filament voltage by about 10 percent but
any decrease in performance is only slightly noticeable. Super-smooth
tuning with large, easy to read dials that are masked for band-in-use
readout make the RBB/RBC series a pleasure to operate. The 600 ohm Z
audio output will easily drive a matched loud speaker but the design
intent was for earphone operation so don't expect thunderous volume.
Sensitivity and selectivity are typical of the best designs of the day.
>>>

>>> The 1940 selling price (to the government) for these incredible
receivers was $2400 each - a staggering amount of money. An internal
examination shows why the price was so high. These rugged, over-built
receivers had to withstand the constant mechanical vibration while at
sea in addition to the mechanical shock of firing multiple 16" guns
(along with firing all of the other artillery present on battleships.)
Also to be rugged enough to hopefully be able to withstand the shock of
a possible torpedo or bomb hit and still keep communications operating.
Since the ship had to supply its own power, the receiver circuitry and power supply stability had to withstand the
severe power fluctuations that happened when gun turrets were rotated.
Additionally, everything had to have maximum shielding to prevent stray
emissions from the LO getting to the antenna and also to allow the RBB/RBC to operate in the presence of other receivers, transmitters and
radar without interference. In many instances, the RBA/RBB/RBC receivers
were so well-respected and their performance so good, they not replaced
with more modern receivers until the mid-1960s - a testament to their magnificent design and construction. Shown in the photo above
is the RBB-2 on the left and the RBC-3 on the right - both built by RCA.
The McMurdo Station Radio Room photo shows three receiving stations. The nearest
(#3) is using rack mount type RBB and RBC. The next station back is set
up with three RBB/RBC receivers and one RBA receiver. The furthest
station back is using two RBB/RBC receivers and one RBA receiver.

Using either the RBB or RBC as the receiver in a vintage
military amateur radio station requires some thought since neither receiver has
any standby function, either on the front panel or remotely. Most USN
operations had the receivers and transmitters on separate antennas and
operating on "split frequency," that is, one receive frequency and a
different transmit frequency. Most ship daily operations were in the
receive mode only anyway. To use the RBB or RBC as a station receiver
will require good isolation between the transmitter and receiver if they
are using the same antenna. A dow-key relay will switch the antenna and
some dow-key relays have an extra switch inside the coax barrel that
further isolates the receiver. Other military type transmitters will
have their own internal send-receive relay. Usually, isolation is good
on these types of TR relays and some will ground the receiver contacts when in transmit.
Check your transmitter's TR relay, if you're going to use it, to make
sure that it does ground the receiver antenna input when in transmit. If
you're going to use an external TR relay then utilize the auxiliary
contracts to achieve a "receiver antenna input ground on transmit." There is a neon
bulb and some other protection circuitry but grounding the antenna input
is good added protection. As to muting the receiver, in CW there's no
need and the receiver can act as a CW monitor. In AM, the gain control
will have to be reduced to mute the receiver if you're using a
loudspeaker. When using a headset, you'll probably hear yourself but you
probably won't experience feedback. There are other methods
to achieve "mute on transmit" but that would require internal additions to the the receiver and then a
control line would have to be brought out the back of the receiver. Not
necessary and it only compromises the receiver originality.

General
Electric - RBD (CG-46132)

The RBD receiver was used with the TCX transmitter as
low-power, two-way communication equipment. The TCX provided CW at 32
watts output power and Voice at 9 watts output power. Antenna was a 24
ft. whip. The RBD receiver was a seven-tube superheterodyne that
provided continuous tunable frequency coverage of 1.5mc up to 12 mc in
four tuning ranges with an additional four crystal-controlled,
fixed-frequency receiving channels that could be selected with a front
panel rotary switch. Crystals were inside metal cases that resemble
metal octal tubes and plug into octal tube sockets on the receiver
chassis. A headset output was provided as well as a separate loud
speaker output - both with individual output level controls. The circuit
uses single preselection (one RF amplifier stage) along with a converter
stage (mixer combined with LO in one tube) and a separate oscillator for
the crystal controlled channels. Three IF amplifiers operate at 915kc. A
combination BFO and Detector/AVC tube is used in the circuit. A single
6V6 provides the audio output. The bottom cover had shock mounts
installed. Power requirement is +12vdc for the tube heaters and +220vdc
for the B+. A dynamotor set-up could be provided for either +12vdc or
+24vdc input. There was also a power supply available for either +110vdc
or 110vac operation. The RBD (and the TCX) were not produced in large
quantity and the serial numbers only go up to 500. The contract dates
from 30 June 1941 however the "acceptance" tag is dated in 1944. The RBD
shown in the photo is original finish with black wrinkle finish front
panel and top, olive-drab sides/back and bare aluminum bottom cover.

When operating the RBD today it's possible that a strong AM
broadcast station operating on 910kc or 920kc might "leak" into
the IF which is tuned for 915kc. Since the RBD has only one RF
amp there isn't too much isolation although the receiver does
have built-in adjustable wave traps for 915kc on the Antenna and
1RF tuned sections. If AM BC stations are being received via the
IF be sure to check the adjustment of these wave traps. The RBD
is a good performer although there isn't a lot of selectivity.
Sensitivity with a short antenna is pretty good. Using a tuned
ham type antenna, e.g., a tuned or resonant dipole, will provide
extra isolation and should eliminate any AM BC leaking into the
IF problems. However, using an untuned large antenna (like an
end-fed wire without a tuner) will only allow strong AM BC
leakage into the IF to happen much more readily. The receiver
was designed for a 24 ft whip and it works best with a fairly
short antenna or a tuned/resonant antenna. Audio output
impedance is 600 Z ohms.

National began
supplying the U.S. Navy with their NC-100A direct dial readout, coil
catacomb band switching receiver by 1940. Designated as RAO, the first
versions are somewhat similar to the standard NC-100XA receivers, which
was introduced in June 1938. The early RAO circuit probably uses 10 tubes and tunes AM
BC up to 30MC and also features a crystal filter, a S-meter, a tone control and a
noise limiter. A 500 Z ohm audio output transformer was incorporated
into the circuit as well, though this was standard procedure for Navy
receivers and it is likely that the very early, first versions of the RAO also had
500 Z ohm outputs. This was to assure that the B+ did not appear on the
speaker terminals as was standard for the civilian National NC-100
series. In fact, standard for the civilian NC-100A receiver was the use
of a field coil type speaker and push-pull audio output, neither of
which the Navy would have on their receivers. Consequently, the RAO and
the RAO-1 should have modified audio output along with an extra filter
choke to take the place of the "field coil used as a choke."
The civilian NC-100XA had push-pull audio employing eleven tubes. Since
the push-pull audio was eliminated on the early RAO, it probably
employed ten tubes.

Before WWII began, the
Navy wanted minimal radiation from the receiver's Local Oscillator on
the antenna. This was primarily to allow the receiver to be used in the
presence of other shipboard radio equipment without interference,
although that probably didn't sound as important as the most publicized
reason, that of stopping enemy direction finding and locating efforts.
Beginning with the second of the numbered suffixes, the RAO-2, National
added an extra RF Amplifer with an additional coil catacomb and tuning
condenser housed in a bolt-on rear chassis and cover. The extra RF Amp
provided the isolation necessary to keep the LO radiation on the antenna
below the designated level of <400pW. The engineering and
design upgrade to add double-preselection (two TRF amplifiers) to the
RAO probably dates from mid-1941. The USCG R-116 receiver contract dates
from May 15, 1941 and it incorporates double-preselection in the same
manner that the RAO-2 does. The second TRF amplifer was set-up for unity
gain, so, ideally, the RAO-2 would have similar sensitivity to the
single-preselection versions. The RAO-2 was also set-up to use the
improved Crystal Filter that had been introduced with National's NC-200
receiver (in late 1940.) This Crystal Filter used a stepped-switch for
Selectivity and a variable condenser for Phasing. With the new Crystal
Filter, the IF was changed to 455kc, the industry standard and the IF of
the NC-200 receiver. The additional RF amplifier increased the RAO-2
tube-count to eleven.

Most WWII equipment was
built under contract and not all RAOs were built by National.
Wells-Gardner Company was the second contractor for the RAO series,
building the RAO-3, 4 & 5. The Wells-Gardner versions were generally
intended for shore stations and, for some reason, the Navy didn't
consider them to be "heavy-duty military-type" construction although the
receivers are nearly identical to the National versions. RAO-2 and RAO-6 receivers
will have an ID from National of NC-120 located on the crystal filter
control nomenclature plate.

Shown in the photo to the left is a Wells-Gardner RAO-3 (115vac
only) from 1943. I found this particular RAO-3 receiver in 1969.
It was a derelict that had been abandoned in a greasy driveway.
Most of the tubes were missing and the interior of the cabinet
filled with small rocks. I took it home for repair and then used
it initially as my first real "ham" receiver making several CW
contacts on the 15 meter Novice band. After 37 years of minimal
use (mostly storage,) the old RAO-3 has recently undergone
another restoration to bring it back to full operation and
first-rate appearance (2006.) This is the same RAO-3 that was
featured in an "Antique Radio Classified" magazine article in
the late 1980s titled "Rios Radio Revisited" and it is also
pictured in Raymond Moore's book, "Communications Receivers -
4th Ed." under National RAO.

1943 - Wells-Gardner Co. - RAO-3 mounted on
original shock mount

National continued on
with the Navy contracts building the RAO-6, 7 & 9 (the designation RAO-8
was not used.) Early RAO-6 receivers had S-meters and are very similar
to the RAO-2. Later RAO-6 versions were equipped for panoramic adapter
use and eliminated the S-meters. The RAO-7/9 receivers were of robust construction and had
increased shielding to further allow their use with other shipboard
equipment without interference. The audio output Z was changed to 600
ohms with the later versions. The RAO-7/9 eliminated the S-meter in
favor of panoramic adapter connections as the late versions of the RAO-6
did. The RAO 7/9 simplified the maintenance of the receiver by
designing the chassis so that it was easily removable from the cabinet
(handles were added to the receiver front panel to assist removal.) The
cabinet itself was redesigned for better shielding and easier mechanical
construction by making it a one piece unit. The early RAOs had used a
separate shock mount system but the new cabinets mounted the shocks
directly to the bottom of the cabinet further easing construction and
maintenance. The RAO-7 & 9 receivers are physically
larger than the earlier versions with full 19" rack width panels
although the receivers are not designed for rack mounting. The earlier RAO
versions are 17.5" wide, with an integral panel-cabinet-chassis
construction that requires major disassembly to service or repair.

The RAO
receivers have impressive sensitivity even though the second RF
amplifier is running at unity-gain. The stability is also
impressive with very little drift after a short warm-up.
The tuning rate is quite fast which was probably
intentional for quick band scanning for signals. The fact that
the later RAOs have provisions for panadaptor operation seems to
confirm that they were used for surveillance rather than
communications. However, much of shipboard radio operations were
in the receive-mode.

The receiver
shown in the photo to the right is RAO-7 SN:J444. This receiver
was destined for the South Pacific and, as a consequence, it was
given a moisture and fungus preventative coating (MFP.) The MFP
was applied to the chassis, front panel tags and knobs giveing
the receiver tags a gold appearance.

The receiver
shown in the top photo is the National RAO-7 SN: 10. The
contract date is Sept. 22, 1943 and the Navy acceptance date is
in 9-30-1944. National-chassis stamped serial number is H720.
This receiver was stored for many years at the Alameda Naval
Air Station in California though it was never installed or put
into service. It is in excellent condition and is an all
original example that functions beautifully.

Restoration details are on the
"National NC-100 Series Moving Coil Receivers" web-article.
Navigation link in Index at the bottom of this page.

National Company, Inc. - RBH Series

The RBH was the Navy designation for the NC-156
receiver, a 10 tube superhet that covered 300kc to 1200kc and 1700kc to
17mc in five bands utilizing National's famous moving coil-catacomb
bandswitching system. The receiver is a version of the NC-100XA that
allowed continuous coverage of the 300kc to 500kc range by having the IF
operate at 1500kc (which is why there is a gap in the tuning from 1200kc
to 1700kc.) The receiver also features single preselection, two IF
amplifiers, crystal filter, S-meter, BFO and tone control. The dial uses
the articulated pointer that indicates band in use by its alignment with
the proper tuning scale on the illuminated dial. The initial RBH
receivers will have "NC-156" on the National Co. nameplate (part of the
crystal filter panel.) The first RBH receivers date from around 1940,
however the receiver required some modifications for use at sea during
WWII and a series of RBH receivers followed. All of the RBH series with
number suffixes, e.g. RBH-1, RBH-2, etc., have an additional stage of
preselection added with a bolt-in chassis and cabinet to house the
additional catacomb section for the coils and an additional tuning
condenser for tuning the stage. This addition was very similar to the
RAO receiver change and was for the same purpose of reducing the LO
radiation from the antenna (>400pW on the antenna.) The dial system
changed on the later RBH receivers, eliminating the articulated pointer
and painting the background white rather than silver. The last of the
RBH receivers incorporated the same improved cabinet of the later RAO
receivers. When operating an RBH today, strong AM-BC stations around
1500kc will resonate with the RBH's 1500kc IF amplifiers and can cause
strong heterodynes when tuning in stations or, if the 1500kc AM-BC
station is particularly strong, it may dominate the IF system of the
RBH. A 1500kc wavetrap on the antenna lead-in will usually cure any
serious problem. The early RBH receiver shown in the photo above
unfortunately has had all of its Navy tags removed. Although the "urban
legend" is that surplus dealer sales required tag removal but this is
unlikely. Another story is that if tags were still on a surplus unit the
government could "reclaim" it because they would consider it stolen
equipment so the new owners removed the tags. Again, hard to believe.
The most likely reason for missing tags is that post-war owners of WWII
surplus gear removed the tags so the equipment would appear to be new
"civilian" models that would impress their friends.

National Company, Inc. - RCK-N

National had been building receivers for airport
communications since 1932 with their contract for RHM superheterodynes.
The HRO was destined for airport use but its many accessories, such as
multiple coil sets, power supply and speaker seemed to limit its
popularity as an "airport receiver." In 1936, National introduced the NC-100 "Moving Coil"
Receiver. Only a speaker was required and the receiver was easy to use
and very durable. By 1937, National had introduced the RCD, an NC-100
especially made for airport communications use. That was
followed by the RCE that had further refinements to airport use. The RCF
and the RCF-2 came along in 1940. During WWII, USN
airport ground-to-air communications required some changes to the
standard National Airway Communication Receiver. The USN needed more
than just the 200kc to 400kc band that had been standard for Airway
receivers. National added 400kc to 800kc to allow the USN full use of
that part of the spectrum since the Navy was particularly in need of
complete coverage of the entire 400kc to 500kc band. The remaining HF
bands cover 2.5mc up to 23.5mc, again, slightly different than the
standard Airway receiver but tailored to what the Navy needed. 12 tubes
are used in the RCK-N with no S-meter or carrier level indicator
supplied. The C.O.N.S. switch is a "Carrier Operated Noise Silencer"
that acted as a squelch control allowing the receiver to operate only
when a carrier was present. Since the receiver covers 200kc to 800kc
continuous, the IF had to be moved from the standard 457kc (for Airways
receivers only) up to 1560kc. Audio output uses a single 6V6 into a 600Z
ohm load. The entire Airway communication receiver line continued with
the RCL that featured a two-position bandwidth switch. After WWII, RCK
and RCL receivers were rebuilt into the RCP and RCQ receivers by
specialized contractors (not National.) The last
National Airway receiver was the RCR from 1948 and it was based on the
NC-240CS receiver.

The model letters RCK were
concurrently assigned to both the National Airway receiver and to a Navy
VHF four channel receiver. Rather than reassign different letters, National's
Airway receiver used a suffix "-N" to differentiate it from the other RCK
receiver.

National
RBL-5

National Company, Inc. - RBL Series

National produced the RBL series of longwave TRF
regenerative receivers for the Navy during WWII. The RBL uses a seven
tube circuit covering 15 KC up to 600 KC in six bands. The tube line up
consists of three cascaded 6SK7 RF amplifiers, a 6SG7 regenerative
autodyne detector, a 6H6 audio limiter with a 6K6G audio output tube and
the 5Y3G rectifier (5U4G in earlier RBLs.) Unlike the RAO that it
resembles, the RBL receiver's bandswitch does not operate a moveable
coil catacomb, instead an intricate set of gears simultaneously actuates
two large ceramic bandswitches. Also unlike many of the WWII longwave
receivers, the RBL series has direct frequency readout on the tuning
dial. The receiver also included a selectable "broad" or "sharp" audio
filter and an adjustable output limiter for operation during intense
static conditions. The limiter control was very well designed and works
wonders at reducing static bursts. Audio output is via the earphone jack
on the front panel and is for 500-600 Z ohm 'phones. Heavy duty
construction through-out and the entire receiver is fully shielded with
a cabinet that is copper plated under the black wrinkle finish. The
RBL-5 shown in the photo is from 1944 and its excellent original
condition is matched by its first-rate performance. The RBL-5 is a great
performer, capable of receiving NBDs from all over North America,
world-wide LW BC, WWVB, JJY, Navy RTTY and almost all other types of
signals in the LF spectrum.The contractors for the RBL Series is
similar to the RAO Series in that National built certain versions and
Wells-Gardner built other versions. (See our "Vintage
Longwave Receivers" webpage for an in depth article about this
receiver.)

Wells-Gardner
Company - RBL-3

As mentioned above, Wells-Gardner Company was
also a contractor for the RBL receiver building the RBL-3 (and
probably the RBL-4.) The W-G RBL-3 is almost identical to those
versions built by National with the exception that W-G used
their own transformers and chokes along with their own sources
for smaller components. Most of the major parts are built by
National so the similarity between the W-G versions and the
National versions is very apparent. Performance is likewise
similar to the National RBL receivers.

National Company, Inc. - HRO Junior Variants

The Navy found little use for S-meters or Crystal
Filters so the HRO Junior receiver, which lacked these features along
with amateur bandspread coil sets, was a good receiver to start with to
create what the Navy needed for various communications and monitoring
functions. First, the Navy wanted an HRO that would tune continuously
from 50kc up to 30mc. The Navy was especially interested in
uninterrupted tuning in the 400kc range. This required National to
re-engineer the HRO IF section to tune at 175kc and also to modify the
LO coils in the coil sets that were supplied with this variant of the
HRO Junior designated the RAS. Seven coil sets were supplied with the
RAS that allowed coverage from 190kc up to 30mc with complete coverage
of the 400kc part of the spectrum. The RAS was installed into a 36" tall
table rack that also included a coil storage unit and power supply.
Sometimes a loud speaker panels is also installed in the rack. Most Navy
HRO racks didn't have loud speakers because nearly all reception was
done using head sets. If you run across any "orphan" coil sets that have
the coil assembly insulator marked with the number range of 5,6,7 or 8,
these are 175kc IF coils and they are for the RAS.

The RBJ is a similar HRO Junior variant that covers 50kc
to 30mc with nine coil sets. Frequency coverage is actually 50kc to
400kc and 480kc to 30mc. The 80kc gap in the frequency coverage is
around the IF of 456kc. The RBJ is also installed in a table rack. Shown
in the photo to the left is the RBJ-2 receiver from a photo in the
manual.

E. H.
Scott Radio Laboratories, Inc. - RCH

Sometimes the RCH is categorized as a
"morale/entertainment" radio for the Navy, however the military manual
makes no mention that the RCH was intended for entertainment and, of
course, the receiver is quite different from the Scott SLR receivers
(including the RBO receiver) that were specifically for shipboard
entertainment use. The RCH tunes from 80kc to 560kc and from 1.9mc to
24.0mc in five tuning ranges. LF coverage implies that the RCH was for
Navy communications. The two tuning ranges (LF and SW) are continuous
coverage within their coverage (the SLR provides AM BC and two
bandspreaded SW ranges.) Also, the receiver has a BFO (so do some models
of SLR receivers) and has the typical mode-selecting determining whether
the GAIN control functions as an RF gain (in the CW mode) or as a AF
gain control (in the MOD mode.) The RCH also provides an output limiter
(CW OL) that removes the AVC and limits the available gain via a pot
adjustment on the side of the receiver chassis. All of these functions
imply that the RCH is a communications receiver. Additionally, two RCH
receivers can be set-up to allow simultaneous reception of two different
frequencies by one operator (PHONE CONTROL.) This was usually done while
"guarding" frequencies, essentially monitoring two different frequencies
for intermittent signals of either enemy or friendly origin. All things
that an entertainment receiver would not be expected to do.

The RCH circuit uses single preselection (one TRF stage)
with two stages of IF amplification and has a total of eleven tubes. The
IF is 585kc, certainly not a standard frequency but it was employed to
allow continuous coverage of the region of the spectrum between 300kc up
to 500kc where the USN did a signification amount of communications (the
standard 455kc IF would not allow operation for about 25kc either side
of the IF thus not allowing coverage of 430kc up to 480kc.) The
selectivity is fixed and determined by the IF bandwidth which is about
8kc at 10 db down. The audio output impedance is either 20K or 600 ohms.
One has to install a jumper on terminal boards located on the side of
the receiver to select either the 20K or the 600 ohms depending on the
listening set-up. Hi-Z phones would use the 20K line but if a loud
speaker or lo-Z phones were used then the 600 ohm line would be
selected. If the 20K line is selected then a 600 ohm load resistor needs
to be installed across the 600 Z ohm terminals. About 2 watts of audio
is available to the loud speaker if used (single 6V6 audio output.) The
audio circuit doesn't have any specific filtering to limit bass response
but overall fidelity is about 70hz to 3500hz at 3db down. One can also
adjust a pot on the side of the receiver to limit the amount of audio
available at the phone jack. The Antenna Trimmer only functions on the
two lowest frequency bands (80kc to 560kc.) There may have been a
specific loudspeaker produced for the RCH but it isn't mentioned in the
USN manual.

Performance is quite good on the lower frequencies but
since there is only a single TRF stage images do begin to show up around
10mc. The larger and more elaborate the antenna system used, the more of
a problem the images will be. An antenna specifically tuned for the
desired frequency of reception will help in reducing images above 10mc.
Sensitivity specifications indicate that Band 3 has the best response at
about 6.5uV at 20db S:N. The other bands are spec'd at around 10uV, so
don't expect to hear the stations that are at the "noise floor." On LF,
I was able to copy FCH 344kc, CC 335kc and MOG 405kc during the day
which indicates that the RCH performs like most LW receivers of the
period when it comes to copying NDBs. On the higher frequencies, SW BC
and AM hams sound very nice. On CW or SSB, the BFO has too much
frequency variability, that is, just a slight adjustment of the control
will result in several hundred hz change. This makes using the BFO for
"fine tuning" SSB difficult. Dial accuracy is superb given that any dial
of the period is going to have limited resolution but "markers" like WWV
are "right on" (provided the receiver has been aligned recently.) No
remote standby is provided so using the RCH as a station receiver will
require some thought. Separate receive antenna would be the easiest
solution but this will require turning down the gain during transmit.
Same with an antenna relay, although there is a disconnect of the
antenna, turning down the gain will be required. On board ship, most
operation was "receive-only" and any transmissions were usually not on
the same frequency as reception, so receiver standby was not needed.

The RCH is a Scott SLR-type receiver in that it is a
low-radiating receiver that produces less the 400 pico watts of LO
leakage to the antenna. This was a Navy specification for all shipboard
receivers that was to prevent the reception of the LO radiation (or
leakage to the antenna) by enemy DF equipment or enemy receivers.
Additionally, SLR receivers would not interfere with other radio gear
and would not be interfered with by other radio gear on the ship. The
large cabinet and shock-mount base is standard for the Scott receivers
and accounts for about 35 lbs of the total weight of 106 lbs for the
RCH. The early RCH dial escutcheon had a white-filled "S" as shown in
the photo above. The "S" was eliminated on later versions of the
receiver.

RBK-1

the
Hallicrafters Co. - RBK series

The RBK Series of VHF receivers were produced for the
USN by Hallicrafters and were essentially their S-27 model. The RBK
tunes from 27mc up to 145mc in three tuning ranges and will receive
signals in AM, CW or FM. The IF is 5.25mc and two selectivity positions
are provided. Audio output is a pair of 6V6 tubes in P-P with 500 ohm Z
and 5000 ohm Z outputs. 15 tubes are used and features three acorn-type
tubes in the front end, 956 RF amp, 954 mixer and 955 LO. As the RBK
series evolved, it followed the S-27 upgrades and eventually became the
S-36 and S-36A versions of the receiver. Many RBK receivers will be the
S-36 version of the receiver but the tuning dial bezel will still have
"S-27" embossed on it. It's generally believed that Hallicrafters used
up all of their S-27 bezel stock before switching to the S-36 bezels.
The later versions of the RBK will have a different S-meter that has a
white scale and is non-illuminated. Also, some very late RBK receivers
will have an extra RF amplifier for increased isolation between the
receiver and the antenna. Most RBK receivers were used with panadaptors
for surveillance and enemy signal monitoring, both on shore and at sea.

General
Electric - TAJ-19

The TAJ-19 was a 500 watt CW and 250 watt MCW transmitter that
operated from 175kc up to 600kc. The transmitter used only four tubes.
The MO was a 860, the IPA was also a 860, the AF Osc was a 860 and the
PA was a 861. The TAJ-19 was powered by a motor generator set up the
provided 1500vdc, 3000vdc (PA plates,) 1200vdc and 115vdc (for
control circuits.) AC voltage was applied to the tube filaments by way
of slip rings that ran on the DC driver motor. The rack, chassis and
panels are all aluminum.

TAJ transmitters were found on most larger Navy ships
during WWII. Though the Navy catalog states that they were for cruisers
or destroyers, they were used on most large Navy ships for Medium Wave
and Low Frequency transmission requirements.

This TAJ-19 was left in my driveway back when I was
still operating the Western Historic Radio Museum in Virginia City. I
had a telephone call some months before from a ham in Washington state
who was "cleaning house." He said the next time he was down in Nevada
he'd drop off some equipment that had been used at Grand Cooley Dam for
guided tours and public address. I never thought too much about it since
it sounded like it was audio gear that was mainly for parts. I really stopped thinking about it
after I didn't hear anything for a month or so. Months later, I was
coming home from running some errands and there in my driveway was a seven foot tall rack full of audio equipment like rack
tape players and speaker panels. Also, a pile of audio cables and
miscellaneous other types of audio equipment. To the side of the audio
gear was the TAJ-19. The fellow had mentioned an old Navy transmitter
that might be good for parts but not what type it was. It was odd that
the guy
didn't "hang around" town since it was Virginia City and there were all
types of distractions (maybe I mean attractions) to pass some time. Not
to mention, I had only been gone for a little over an hour. Perhaps he
was in a hurry and just "dumped" the gear and left. Anyway, I never
heard from him again.

Now, this TAJ-19 is not complete. It has been severely
scavenged for parts over the years. I'd estimate that around half of the
transmitter is missing. But, the cabinet and the panels are excellent
and complete with knobs, meters, switches and even all of the data
plates. Only the very bottom front panel is missing. The sides, back and
top are all present. The various chassis are present. Even a couple of
the 860s are still installed. So, while this particular
TAJ-19 will never again be operational, if another TAJ-19 ever showed up
around here, who knows? Maybe between two of them, one functional
transmitter could result. Of course, Medium Wave and LF CW for the
amateur is somewhat limited with only two bands approved at this time -
630M and 2200M.
630M or 472kc to 479kc allows CW and data operation with a 5 watt EIRP
limitation. It's not as low of power as one would think. Due to the
inefficiency of most ham antennae at low frequencies, the effective
radiated power can be rather low even though the input power is
relatively high. Think of a dummy load. You can input a lot of power
and it radiates very little. Most antennae on 630M are something like
the dummy load. The typical ham antenna on 630M would have about 400
watts input before the EIRP would be about 5 watts. So, there may be hope for an operational TAJ-19,...if one can
figure out how to power it up without the shipboard power and the
motor-generator set-up. A homebrew AC power supply is the most likely
solution.

The Collins T-47/ART-13 is a 100 watt carrier output,
AM-CW-MCW transmitter that was generally used in USN and USAAF/USAF
aircraft but could also be found onboard USN ships as the TCZ
installation. There were even some vehicular uses for the T-47/ART-13.
The T-47/ART-13 was developed from the earlier Collins ATC Navy Aircraft
Transmitter that appeared around 1940. By 1942, Collins was building the
T-47/ART-13 for installation in Navy aircraft and other applications.
The USAAF also wanted to use the T-47/ART-13 and a very slightly
different transmitter was produced for their use, designated as the
T-47A/ART-13. Many of the T-47A/ART-13 transmitters were built by
contractor Stewart-Warner. Documentation was changed near the end of
WWII to designate the transmitters as AN/ART-13 with the A suffix
included. When combined with other equipment the set-up designation is
for the entire installation. Hence, the combination ARC-8 describes the
ART-13 combined with a BC-348 receiver along with the other necessary
auxiliary equipment for a complete aircraft radio installation.

The T-47/ART-13 power requirements were supplied by a
dynamotor that ran on the aircraft +28vdc battery/charger system. The
aircraft battery buss supplied the +28vdc@10Amps necessary for the
transmitter's tube filaments and relay operation while the dynamotor
provided a dual output of +400vdc and +750vdc. The dynamotor would have
the two B+ levels connected in series for the HV Plate ( +1150vdc) below
20,000 to 25,000 feet altitude but a barometric pressure switch (located
inside the dynamotor housing) would separate the outputs at higher
altitudes and only allow +750vdc maximum to prevent arc-over. There were
at least three types of dynamotors used, the DY-17, the DY-11 and the
DY-12 (after WWII an improved DY-17A was produced.) The shipboard TCZ
featured two types of power supplies, a 115vac operated power supply (of
enormous proportions) that supplied the required +28vdc, +400vdc and
+1150vdc directly to the transmitter Additionally, the 115vac unit had a
motor-generator that provided +14vdc and +28vdc (the +14vdc was required
for relay operation inside the ac or dc operated TCZ power supply.)
The115vdc operated TCZ power supply used two dynamotors that ran on
115vdc input and provided +14vdc and +28vdc output on one dynamotor and
+400vdc and +1150vdc on the second dynamotor. The USMC had a vehicular
set-up that installed an ART-13 transmitter with a BC-348 receiver that
operated from the back of a Jeep and ran on the +28vdc battery system
with HV provided by a DY-12 dynamotor. The antenna used was a whip.

The T-47/ART-13 featured an advanced Autotune system
that would automatically tune up to 11 preset channels (10 channels plus
one LF channel) selectable by a front panel switch. The Autotune system
would tune the transmitter frequency and output network to mechanical
presets that then would match a properly selected antenna. The Autotune
cycle took about 25 seconds to complete. Switch position MANUAL would
allow manual adjustment of the tuning without disturbing the Autotune
presets. The T-47/ART-13 uses an 837 as the variable frequency
oscillator, two 1625 tubes are used as multipliers, an 813 as the power
amplifier and two 811 tubes as the P-P modulators. There are also two
small modules. One provides the audio amplifier and sidetone amplifier
using two 6V6 tubes and a 12SJ7 tube and the other module, the
MCW/Frequency Calibration Indicator, uses two 12SL7 tubes and a 12SA7
tube. FCI allows the operator to calibrate the frequency of the
transmitter by providing a 50kc calibration signal derived from a 200kc
crystal oscillator. The transmitter frequency range is from 2.0mc to
18.0mc, however many Navy T-47/ART-13 transmitters were equipped with a
plug-in Low Frequency Oscillator (LFO) module that allows the
transmitter to operate from 200kc to 600kc or 200kc to 1500kc (at
somewhat reduced power, CW only.) Early LFOs have a frequency range of
200kc to 1500kc in six ranges while the later LFOs cover 200kc to 600kc
in three ranges. The LFO module uses a single 1625 tube. There are some
indications that the Navy preferred the 200kc to 1500kc LFO while the
USAAF used the 200kc to 600kc LFO. Many versions of the T-47/ART-13 will
have a blank plate installed where the LFO module was installed (along
with a resistive load substitute for the LFO's 1625 filament.) After
WWII, the USAAF/USAF didn't use the LFO module but the USN still did.
This statement is according to the USAF Extension Course 3012 book on
"Radio Mechanics" although this book is from the 1950s and may reflect
the uses of the LFO at that time rather than during WWII. Many
transmitter installations also used a separate antenna tuner and three
selectable condensers to allow easier loading into various antenna
impedances at lower frequencies. Also most installations on aircraft
included a small Remote Control Panel that allowed the pilot to operate
the transmitter from the cockpit. There are a couple of different
remotes and antenna tuners that were used with the ART-13.

To the right is a photo showing the chassis of
the Collins-built T-47/ART-13. This transmitter has the Navy
version LFO installed. Also, this is a fairly early version of
the transmitter so there are some differences when compared to
the T-47A/ART-13 versions. Of note is the lack of an interlock
switch which on the early versions allows you to easily operate
the transmitter with the lid off. The module to the lower right
is the Audio Amplifier unit and directly behind it is the 837
VFO tube. Behind the VFO tube is the FCI/MCW module and to the
left of it are the two 1625 multiplier tubes. The module in the
center of the transmitter is the LFO. In the section at the rear
of the transmitter, to the left side is the modulation
transformer from which its plate leads connect to the two 811
modulator tubes. To the right of the 811s is the 813 PA tube.
The left-center section of the transmitter contains the matching
network and the LF relay (next to the LFO module.) On the far
left is the vacuum TR switch and behind it is the keying relay.
The round ceramic unit in front of the vacuum TR switch is the
inductive pickup for the Antenna Current meter.

The somewhat
later USAAF T-47A/ART-13 version added some minor improvements
to the transmitter with a vernier scale on the VFO Fine Tuning,
a top lid interlock switch, a different bottom plate with
built-in guides for the shock mount and a white ceramic
insulator bell on the antenna connection being among the most
apparent changes. There was also a T-412/ART-13B that added a
selectable crystal oscillator in place of the LF module. The
crystal oscillator normally has 4 LF/MF channels and 20 HF
channels. All ART-13Bs are retrofitted earlier models and it is
possible to find even an early ATC transmitter that has been
converted to the ART-13B version.

photo above: Chassis of the Collins
USN T-47/ART-13. The MCW/FCI module is the later, three tube
version. The Collins chassis are usually painted gray and have a
"winged emblem" embossed near the 837 VFO tube.

photo above: USAAF T-47A/ART-13,aka
AN/ART-13A. Note the blank panel installed to replace the LFO.
Also note that the two meters do not match. This is very common
to find on many ART-13 transmitters and was probably a result of
depot repairwork.

The T-47/ART-13 and its variations had a very
long life. Introduced around 1943-44, actively used during and
after WWII and well into the fifties (sometimes found still
being used well into the sixties and early seventies.) The USSR
also produced a copy of the ART-13 that they used up well into
the 1980s (the R-807.) Because of its long useful life, most
T-47/ART-13 transmitters found today will have had many
scratches and a few dents and paint scrapes. Sometimes
non-matching modules will be encountered with some parts having
MFP applied and others that are bare. A book containing brief
instructions and the calibration settings for specific
frequencies is usually stored in the metal pocket underneath the
transmitter. This book is also usually missing on most
transmitters although the same information is in the standard
manuals. Luckily, thousands and thousands of T-47/ART-13 were
built and spare parts are very easy to find which allows for the
fairly easy restoration and maintenance of these durable and
potent transmitters.

Nowadays, the T-47/ART-13 is finding increased
popularity as a very practical ham transmitter for vintage
military station operation. The transmitter can provide plenty
of power and excellent audio allowing many military radio
enthusiasts to use their T-47/ART-13 station for regular AM net
operation also. The HV can be safely increased to around
+1400vdc to provide even more output power and some brave users
will run the HV up as high as +2000vdc (not for the timid and
distortion might be encountered at this level of HV.) This
assumes that the user is building an AC operated power supply
rather than using the "hard to find" original dynamotor or the
impossible to find TCZ power supply.

The Audio Module has a "fixed-level" gain setting that was designed
to work with specific WWII vintage military microphones. There are two
microphone problems that are normally encountered - first, the military
expected the radio operator to "scream" into the microphone. After all,
he was trying to talk over the aircraft noise and was probably being
shot at! After WWII, many ART-13 audio modules were modified by changing
the carbon mike bias resistor from 15K down to 4.7K. In fact, the
ART-13B schematic shows the resistor value as 4.7K. Modified audio
modules have no problem providing plenty of carbon mike response. An
easy way to
achieve proper modulation levels is to use an Astatic TUG-8 stand with a
D-104 or 10-D microphone "head" (with "DYNAMIC" selected on the Audio Module.) These
mike stands have a built-in, adjustable gain amplifier that provides
ample audio output to drive the fairly low input Z of the T-47/ART-13 (~
500Z ohms.) An oscilloscope should be used to monitor the transmitter
output when trying out different mikes as it will be very apparent on
the 'scope whether proper modulation is being achieved. Due to the
unbalanced, low reactance typical ham antennas used on 80 and 40 meters,
the T-47/ART-13 will require an auxiliary capacitor connected to the COND terminal to ground for proper loading of these kinds of antennae.
These external capacitors should be high voltage rated ceramic types. A
large air-variable can also be used.

For more details and
information on the Restoration and Operation of ART-13 Transmitters go
to our web-article "ART-13 Transmitter - Restoration to Complete and
Operational Condition" - below in the Navigation Index

photo above: Chassis of the AN/ART-13A. Note the
"gold" appearance from the MFP coating.

U.S. Navy
Shipboard and Shore Entertainment Receivers

SLR-F
Receiver with BFO

E. H.
Scott Radio Laboratories, Inc. - SLR Series, RBO Series

During WWII, Scott Radio Laboratories was contracted to
design and build a type of military marine entertainment receiver that
had very low Local Oscillator radiation or leakage to the antenna
system. Scott advertising of the time indicated that the Navy was
concerned with the possibility that enemy submarines could tune in a
superheterodyne receiver LO signal and determine a ship's position with
direction finding equipment. The Scott ads further stated that enemy DF
equipment was sensitive enough to detect LO signals up to 100 miles
away. While this all may have been theoretically true, the primary
reason for the installation of low radiating receivers onboard ships is
that any receiver has to operate in the presence of the several other
receivers, transmitters and sometimes radar equipment that would also be
in use on the ship. None of the receivers can cause interference with
ship equipment and they must be able to perform their function without
interference from other ship equipment. The USN specification was "less
than 400 pico watts" was to appear on the antenna from local oscillator
leakage. The "Scott Low Radiation" Receiver, or SLR, was built to
operate in such a shipboard environment with no interference. The Scott
SLR receivers tuned the standard AM Broadcast band and two bandspreaded
Shortwave bands. They were designed as a stand-alone receiver capable of
high quality reception and wide range audio reproduction via its
powerful push-pull 6V6 output stage.

The multi-tap output transformer allowed matching to
virtually any impedance that might be encountered with 600 ohms
being the most commonly encountered. The receiver's output could
be distributed throughout the ship via the 600 ohm line or it
might be matched to the distribution amplifier for the ship's
audio system. Each ship had different requirements and the Scott
was designed to work with just about any of the ship
speaker-audio systems. Single preselection, two IF amplifers and
a Noise Limiter were included. A BFO was also included in case
the receiver had to double as a communications receiver. When in
the C.W. position, the AVC is disabled and the Volume control
actually controls the RF-IF gain so the signal to BFO injection
ratio is correct. A cathode-ray "tuning eye" tube was also
included in the SLR version.

Not all versions of the SLR
receiver will be equipped with a BFO. If the BFO is not
installed then the data plate is mounted where the CW OSC
control was.

photo left: Scott SLR-12-B. This version
doesn't have a BFO. This SLR is complete but awaiting
restoration.

Scott also built the RBO receiver, a similar looking set but
without the push-pull audio and without a BFO. Parallel
rectifiers are used in the RBO and sometimes the receiver is
seen with a drop-down dial cover - a hinged metal piece that can
be raised up to entirely cover the illuminated dial. The RBO
generally was used for local entertainment within a limited
space (one room) since the single 6V6 audio output didn't
provide enough power to drive the the ship's 600 ohm line
directly (it could run the distribution amp though.)

Both the SLR and the RBO
receivers were installed in a very large metal cabinet that was
shock-mounted to a substantial base mount.

Scott built many
different versions of these high quality "entertainment"
receivers. The receivers were installed not only on U.S. Navy
ships but also merchant ships, tankers, transports and other
types of American vessels.

photo right:
Scott RBO-2. This version has single-ended audio and no BFO.
This particular RBO-2 was rebuilt by Mare Island Naval Shipyard
in the early 1950s. The panel and cabinet were repainted light
grayish-cream color and the nomenclature masked to preserve
readability. The metal data plate located under the "eye-tube"
is the Mare Island "rebuild" tag.

Scott
Radio Laboratories, Inc. - SLRM Marine Receiver

The SLRM is a twelve-tube shipboard receiver that operates on 115 volts AC or
DC. The construction is unusual in that aluminum is used for
chassis, the shielding and the cabinet. This reduces the
receiver's weight significantly - weight is around 50 lbs.
Single pre-selection is used with two IF stages. An ineffective BFO and
a clipper-type Noise
Limiter are provided. Selectable bandwidths are available. The RF gain
is controlled by the AVC when MOD bandwidths are selected but the RF
gain becomes a manual control if CW is selected. Frequency
coverage from .54mc up to 18mc. Push-pull 25L6 tubes for the
audio output. The 1629 "eye tube" only operates when AVC
is controlling the receiver sensitivity in MOD modes. In CW, the 1629
will remain "on" but the "shadow" will not respond to signals since the
AVC is disabled. The panel speaker is 5" in diameter but there is a
multi-impedance-taps output transformer for external loads. The panel
speaker can be turned off if an external speaker is used.
Onboard the ship, the audio output would have been connected to
distribute the receiver output as necessary.

Performance is quite good for AM signals. In the HF bandwidth
AM BC signals or strong SW BC signals sound great if a large
diameter, matched external
speaker is used. The SLRM was primarily an entertainment
receiver, not a communication receiver.

On the downside,...there will be many problems encountered when operating the SLRM. Images become
very apparent around 15mc. SSB and even CW performance is very poor,
if not impossible.
The SLRM may as well not have a BFO since it doesn't function
adequately. The BFO tube is only running +10vdc on the plate
(the 220K ohm plate load resistor significantly drops the B+) and then the BFO circuit is electrostatically-coupled to the detector
which results
in a totally useless BFO. It's likely that because of the SLRM's
all-aluminum construction there was more RF leakage than the
<400pW specification. Scott obviously intentionally reduced the BFO output until the
RF leakage was <400pW probably figuring that the SLRM was going to be for shipboard entertainment where the
barely-functional BFO shouldn't pose any problems. Nowadays, it's very
easy to replace the 220K BFO plate load resistor with a resistor value around
5K which
will increase the plate voltage on the BFO tube to around +85vdc.
This increases the rms voltage of the BFO output to the point
where SSB and CW demodulation is possible. The RF Gain will
still have to be reduced to the point where the signal to BFO
injection ratio provides good demodulation.

IMPORTANT NOTE:
Another significant problem is the SLRM's AC-DC power input which MUST
NOT be operated with the original 3-wire "twist lock" plug and a modern grounded (3-wire) AC power plug connected
directly to the house AC line. To do so will connect the line
return power wiring directly to chassis which prevents the dial lamp
from lighting and takes some of the bias voltages to chassis. Modern
house AC wiring has neutral connected to ground (at the breaker box) and
this will conflict with the receiver power input wiring that assumed the
two AC lines would be "floating." To safely operate the SLRM (or any
AC-DC receiver) requires the use a 1:1 isolation transformer. This provides
the "floating" two-wire AC plus separate chassis ground that the SLRM
design anticipated. The isolation transformer should use a three-wire
cable/plug on the input side. The input side ground pin should be wired
directly to the transformer's output socket
ground pin only. The AC output of the isolation transformer
winding will be "floating" which allows the use of the
original three-wire power
cable and twist-lock plug that grounds the chassis but not either of the "floating"
AC lines. The original power cable on the SLRM used a three-wire "twist-lock"
(actually, two wires and a shield-ground) which can still be used if powered with an isolation transformer set-up
as described. Be sure to have an "ON-OFF" switch on the AC input to the
isolation transformer. This can also be operating the isolation
transformer from a switchable three-wire power strip. If the isolation
transformer is left connected to AC and to the SLRM, then the two line
bypass capacitors will be passing a small amount of current to chassis
ground - even if the SLRM is turned off (check the schematic.)

TecRad
LRR-5 from 1945

Technical Radio Company (TecRad) - LRR-5

Technical Radio Company was founded in San Francisco,
California in 1937 by Clayton Bane and George Weiss. Bane was an
assistant to Frank Jones at Western Wireless, Ltd. (1932 to 1934) where
he helped install the first two-way radio system at Alcatraz Federal
Prison. Many of Bane's crew at Western Wireless went onto work at
Eitel-McCollough (Eimac) but Bane went on to form his own company called
Technical Radio Company. TecRad (as it was sometimes called) became a
prime contractor for the U.S. Navy building high quality shipboard
entertainment receivers and a couple types of small transmitters. Only a
few companies built Navy acceptable shipboard entertainment radios since
there was a strict requirement that no more than 400 pico-watts of LO
leakage was allowed on the antenna. TecRad claimed that only 100 pW was
present on the antenna with their receivers. Scott Radio Laboratories
built the SLR and RBO receivers that are the most common of the "low
radiation" WWII shipboard entertainment receivers but TecRad also
produced their versions during the war designated as "LRR" with numeral
suffixes from 1 up to 6 (LRR = Low Radiation Receiver.) The TecRad
receiver shown is the Model LRR-5 from May 1945.

The LRR-5 is typical of the WWII shipboard entertainment
receivers in that robust, high fidelity audio is delivered to selectable
multiple output impedances (six impedances from 16 ohms to 800 ohms)
since many ships had various kinds of audio loads depending on the size
and layout of the audio distribution within the ship. A front panel
speaker switch is provided to allow disconnecting specific speaker lines
depending on how the ship's speaker system was wired. Most systems
probably had the speaker switch wired to allow the local radio room
speaker to be disconnected while the ship's audio system remained on. 15
tubes are employed in the LRR-5 including an 0C3 voltage regulator and
push-pull 6V6 audio output tubes. Also, a 6E5 cathode ray tuning
indicator tube is provided. The frequency coverage is typical of
shipboard entertainment receivers with the AM-BC tuned with Band 1, Band
2 tuned from 2.0mc to 6.5mc and Band 3 tuned from 6.5mc up to 18mc.
Also, a very accurate logging scale is provided. Single preselection is
used along with two IF amplifiers with three selectivity bandwidths
available. A phonograph input is also provided. Like some of the Scott
Radio Labs' SLR/RBO receivers, a BFO is included - just in case the
receiver might be needed for CW reception and a Send-Receive switch is
provided - just in case the receiver had to be used for two-way
communications. Unlike the Scott receivers, the LRR-5 includes separate
RF and Audio Gain controls thus when the BFO is tuned on, the RF Gain
must be reduced and the Audio Gain increased for proper CW reception.

Performance of the LRR-5 is impressive. The audio is high quality and
with push-pull 6V6 tubes in the output there seems to be quite a bit of
power available. Bass response is very good and Shortwave Broadcast
stations that are playing music sound incredible. AM-BC sounds very good
with plenty of sensitivity available - after all, you might be trying to
"pull in" an American AM-BC station while in the middle of the Pacific
Ocean. Although only a single RF stage is provided, images are not
apparent in normal reception above 15mc as would be expected. Alignment
of the front end provides L and C adjustments for all three bands and
the IF transformers are permeability tuned. Strategic shielding is used
to keep the LO leakage down so there are a few shielded boxes in the
receiver's front end. High quality Peerless transformers (Altec-Lansing)
are used in the LRR-5. One has to also note the perhaps intentional
resemblance that the LRR-5 has to receivers built by Mackay Radio and
Telegraph Company around the same period. The LRR dial material is
exactly the same opaque white plastic (side illuminated) that will
glow purple with intense rear lighting and the gray panel with white
nomenclature is quite similar to that period Mackay receivers. Perhaps
it was intentional so that the LRR-5 would fit in with Mackay Radio
equipment that was in use on many ships.

In 1948, Clayton Bane stated that due to some personal
reasons and due to the fact that his building lease was not going to be
renewed he was closing down TecRad. According to Bane the company was
profitable but there was also some difficultly in that the Navy wanted
TecRad to remain exclusively a Navy Contractor and not be able to
produce for the civilian market. Bane went on to form a successful
advertising business. Bane died in 2003.

Minerva
Corporation of America - W117 "Tropic Master"

The Minerva Tropic Master is an eight-tube receiver that
covers AM-BC and provides one Shortwave band, 5.5mc to 18mc (there are
some minor variations in the shortwave coverage with different
production runs.) The cabinet is metal and features a fold-down front
cover along with a carrying handle. The Tropic Master is an AC-DC
powered receiver. There were two circuits used with the earlier version
having push-pull 50L6 tubes and a series-parallel filament string. This
version could also be modified to use two 25L6 tubes by changing the
filaments to series making the entire string a series load. NOTE:
The schematics in Riders VOL. XV have several errors including the 50L6
filament connection. The later circuit uses two 50A5 tubes and a 35Z5
rectifier. The P-P audio seems a bit much for the small built-in PM
speaker. Four controls provide Volume and ON-OFF, Tone, Band Select and
Tuning. The rear panel of the cabinet has a door to allow access to the
power cord and the antenna terminals. The Tropic Master didn't have
enough shielding to be used onboard ships as the LO leakage would have
exceeded the minimum acceptable level of 400pW on whatever antenna was
used with the receiver.

photo above: The Tropic Master with the front closed

Minerva advertised that they had supplied the
Tropic Master to the military (both Navy and Army) as a "Morale
Radio" - that is, a radio primarily for entertainment in
barracks or other shore locations. Apparently, a few Tropic
Masters did serve in that capacity as there seems to be enough
first-hand accounts to believe Minerva's advertising was
essentially true. Certainly though, the majority of Tropic
Masters were sold post-WWII. The selling price was $75 and many
were sold out of the PXs at various military bases during
late-1945 and through 1946. The Minerva W117 schematic in
Riders' VOL. XV is dated June 1945 and this data shows the two
different versions that are documented. There are apparently
other minor variations that were incorporated into the receiver
circuits but these were not documented.

The Tropic Master receivers have quite a
following and there is ample information available on the
Internet. The Tropic Master (T-M) shown is the second one I've
owned. This currently-owned T-M was found at a Hot August
Nights' Swap Meet (a car swap meet in Reno) about 12 years ago.
I saw it there one year and passed it up because of the asking
price was $80. Next year, to my surprise, there was the same
seller with the same T-M - this time for $50. I purchased it
since I had always regretted the fate of my first T-M. My first
T-M was given to me for shortwave listening when I was fifteen
years old by Phil Rios of Rios Radio-TV Shop, my old mentor in
radio repair (where I had worked summers as a teenager.) I never
did get it to work because, like many of these receivers, the
25Z6 rectifier was missing and, in the mid-sixties, the 25Z6 was
difficult to find (read - expensive, for a teenager.)
Eventually, I used the cabinet for a power supply and lost the
chassis in one of several moves. Luckily, my currently-owned T-M
is in excellent original condition and does function (filter cap
replacement was necessary though.) This receiver is the earlier
version with the P-P 50L6 tubes with parallel filament
connections.

The
Crosley Corporation - REO

Crosley seemed to have most of the WWII contracts for
the smaller "Morale Radios" destined for shore use. Though the Scott
SLRs and RBOs along with the TecRad LRRs could and were used aboard
ships, the smaller radios were generally designed to be less expensive
and this usually resulted in excessive LO radiation which prohibited
their use aboard ship. Though some of the more elaborate "Morale Radios"
for shore use were sometimes found in metal cabinets (like the Tropic
Master above,) the REO is housed in a wooden cabinet that is painted
Navy gray. This simple radio covers AM BC only. The controls are left to
right, Volume, On/Off and Tuning. The Navy wanted to be sure that every
user was aware that the REO was strictly "land use only" and provided a
large red warning tag stating so ("Unsafe Radiation Limits" refers to
the radio's Local Oscillator signal radiation from the antenna and
elsewhere in the circuit since the cabinet provides no shielding.)

WWII U. S.
Navy Contractor Designators

During WWII most U.S. Navy equipment built for the war
effort was manufactured or assembled by contactors. Many times the items
built would be a specific product model of a particular company and
would have exactly the same company parts and same assembly techniques
but the item was assembled by a contactor company. The contactor-built
equipment had to meet the same specifications and therefore most of the
time the equipment performs exactly the same as another example built by
the original manufacturer or another contactor. Each contactor or
component supplier had a specific letter identification that was
incorporated into the specific model number. So, if a piece of Navy
radio equipment is ID'd as CFT-43600, then that piece of equipment was
built by Federal Telephone & Radio Corporation. To the right is a list
of designators used for some of the popular contactor and component
supplier companies during WWII.

CAN - Sangamo
Electric

CAW - Aerovox

CAY - Westinghouse

CBN - Central Radio Labs

CCT - Stromberg-Carlson

CD - Cornell-Dubilier

CFN - Farnsworth Televison &
Radio Corp.

CFT - Federal Telephone & Radio
Corp.

CG - General Electric

CHH - Arrow-Hart Hagerman

CHL - The Hallicrafters Co.

CHS - Sylvania (vacuum tubes)

CJC - Howard B.
Jones

CKP - Air King
Products Co., Inc.

CKR - KEN-RAD (vacuum tubes)

CLF - Littlefuse Labs

CMA - P.R. Mallory & Co.

CMC - Clarostat Mfg. Co.

CME - Radio Manufacturing
Engineers, Inc.

CN - NEMS (National
Engineering Machine Shops)

CNA - National Company Inc.

CND - Andrea Radio Corp.

COL - Collins Radio Co.

CPN - Panoramic Corp.

CRA - Utah Radio Products Co.

CRC - RCA (Vacuum Tube
Division)

CRV - RCA-Victor
or RCA Mfg. Co.

CSF - Sprague Specialties Co.

CTD - Tobe Deutschmann Corp.

CWQ - Wells-Gardner Co.

CWS - Stewart-Warner

CYM - Yaxley-Mallory

CZC - Scott Radio Laboratories,
Inc.

CZR - Zenith
Radio Corp.

NAVY-RADIO.COM
- For the most detailed information WWII Navy gear and on all types and
all vintages of Navy radio equipment, radio stations, vintage
photographs - go to
www.navy-radio.com Nick England's incredible Navy-Radio
website has the most information available.

Radiomarine
Corporation Shipboard Radio Equipment from WWII (not built for USN)

Radiomarine Corporation of America - AR-8506-B

The RMCA AR-8506-B was introduced during WWII with
schematics dated November, 1942 and with the FCC approval for shipboard
use dating from February, 1943. The AR-8506-B is a five band receiver
capable of reception of LF signals from 85kc up to 550kc and
medium/shortwave signals from 1.9mc up to 25mc. The circuit is
superheterodyne and uses 10 tubes along with a NE-32 (G-10) neon lamp
for voltage regulation (LO.) The IF is 1700kc in order to allow the
receiver to cover the entire 400kc range without interruption. Much of
the ship's communications were in the frequency range of 400kc to 500kc
and a standard IF of 455kc would have a gap in frequency coverage from
about 430kc up to 475kc due to the IF operating at 455kc. Usually,
shipboard superheterodynes will have IFs that are in the AM BC band area
since this region of the spectrum wasn't normally tuned by the ship's
communication receiver. The receiver can be powered by 115vdc or 115vac
and can also be powered at 230v ac or dc using an external resistor
unit, the RM-9. Tuning uses a 30 to 1 reduction vernier drive
(counter-weighted) and there is an additional "band spread" function
using a separate control. A built-in loudspeaker is front panel mounted
and can be switched off by the operator if necessary. The FCC approval
for shipboard use indicated that the AR-8506-B's LO leakage to the
antenna was <400pW and thus would not interfere with other shipboard
radio equipment and would not radiate a signal of sufficient strength
for enemy DF or detection. The U.S. Army Signal Corps issued a manual,
TM11-875, giving the AR-8506-B the designation R-203/SR.

These receivers were integrated within a
shipboard communications console, generally the 4U, that
contained two transmitters, another receiver capable of VLF
reception (AR-8510,) an emergency receiver (crystal detector
receiver,) a power control switching system that allowed battery
operation or ship's power operation, motor-generator operation,
various alarms and other equipment necessary for radio
communication at sea. Most 4U consoles were installed on Victory
ships and other merchant ships during WWII.

Shown to the right is the RMCA 4U marine radio unit. Note the
the receiver to the left of the typewriter is the MW-SW
receiver, the AR-8506-B, and the receiver to the right of the
typewriter is the LF receiver, the AR-8510. The two transmitters
are mounted directly above the receivers.

Photo is from "The Radio Manual" Fourth Edition.

After WWII, the AR-8506-B continued to be offered by RMCA for
maritime use on various types of ships. The post-war versions
are somewhat different in appearance in that the individual
celluloid control identification plates are replaced with a
"raised letter" type of panel nomenclature. Additionally, the
data plate was removed and the manufacturing information became
part of the front panel nomenclature. The AR-8506-B shown in the
photo below-right is from 1953 and shows how the later versions
looked when installed in the table top cabinet (with shock
mounts.) The earlier (WWII - from June 1943) style receiver,
using the round celluloid control ID plates, is shown in the
upper photo. Ship owner's reluctance to replace radio gear had
the RMCA consoles and the associated equipment in-use well
beyond their normal life-span with examples still in use as late
as the 1980s.

The AR-8506-B has an internal 1700kc wavetrap.
The wiring and adjustment of the wavetrap should be checked if
BC signal leakage is encountered. The wave trap should be
adjusted on Band 3 for minimum response with a 1700kc RF signal
input to A1 on the antenna input of the receiver. If it is
correctly adjusted and still there is BC signal leakage then
using an antenna that is "tuned" for the specific frequency
desired should be tried. This could be a resonant antenna cut
for the specific frequency desired or an antenna with an antenna
tuner. The "tuned" antenna will be selective and should reduce
the BC interference. Like a lot of RCA receivers, the AR-8506-B
doesn't have a standby switch (either remote or panel.) Most
shipboard radio operations are receive on one frequency and
transmit on another frequency using separate antennas so a
standby wasn't really necessary. To use as a ham station
receiver operating on the same frequency as the transmitter
requires either an antenna relay with good isolation for the
receiver in "transmit" or you can also use an electronic TR
switch. In either case, you'll have to reduce the RF Gain and AF
Gain or switch off the loud speaker.

Radiomarine Corporation of America - Model AR-8510

The AR-8510 is a five tube regenerative receiver that tunes from 15kc up
to 650kc in four tuning ranges. Two TRF amplifiers are used with a
Regenerative Detector and two stages of audio amplification. The RF
amplifiers use a combination of tuned grid and tuned plate with a
three-section ganged condenser for tuning. The audio output can drive
the panel mounted loud speaker or headsets. The panel speaker can be
switched off if only a headset is desired for reception. The receiver
requires a separate power source of which many types were available.
Various types of battery combinations could be utilized with either the
RM-2 or the RM-4 Battery Control panels. These functioned on ships that
provided 115vdc or 230vdc power. If 115vac was to be used then the RM-23
Rectifier Power Unit (power supply) was used. There was also an RM-37A
Receiver B+ Supply Unit that provided 90vdc output from the ship's
115vdc power. This was to be used if it was necessary to conserve the B
batteries that normally provided the +90vdc for the B+. The AR-8510
requires 6.3 volts at 1.8A (AC or DC) and 90vdc at 15mA. The vacuum
tubes needed are four 6SK7 tubes and one 6V6G or GT.

The AR-8510 was
provided with a cabinet and shock mounts if it was to be used as a
"stand alone" receiver. However, if it was going to be installed into a
shipboard communications console (as most were) then the cabinet and
shock mounts were not provided. Many AR-8510 receivers were part of the
shipboard 3U transmitter console that included a 200W transmitter, an
emergency crystal receiver, a battery charger switching panel and an
automatic emergency alarm receiver. 4U consoles used the RMCA AR-8506 (a
MW and SW superhet) and a 500W transmitter. The 5U console had both the
AR-8506 and the AR-8510 installed along with all of the other auxiliary
equipment. Mackay Radio supplied MRU-19 or MRU-20 consoles with their
equipment installed.

The AR-8510 was approved by the FCC for shipboard use in
1942. The schematic drawings are dated 1943. It's likely that it
was at least 1944 before any AR-8510s were in use. The AR-8510
shown in the photo above is dated NOV 1944 and has a serial
number of 2774 making it an early version of the receiver. It
was more than likely installed in an RMCA console so it doesn't
have a cabinet. However it does have a bottom cover that
incorporates embossed dimples for feet that allow the receiver
to set on a table without scratching.

Most of the WWII installations were onboard Liberty ships.
Post-WWII use was for commercial shipboard use. Later versions
of the receiver look like the B&W photo to the right. This is
from the 1950 manual. Note the "raised letter" nomenclature
which is not used on earlier versions. Ease of maintenance
during WWII would have had the receivers fitted with the
celluloid tags that could easily be removed for repainting the
panel or replacement if damaged. After WWII, the "raised letter"
panels were probably used since the receiver wouldn't have to
endure the rigors of war-time use. Post-WWII use continued for
quite some time with AR-8510s showing up on old oil tankers as
late as the 1980s.

photo right: The AR-8510
as shown in the 1950 manual.

U.S. Army
Signal Corps

National Company, Inc. - NC-100ASD

National introduced a
well designed, direct-reading dial for their NC-100 series receivers in
June, 1938. The "A" version dial had a mechanically articulated dial
pointer that indicated the band in use when switching ranges and also
included an S-meter as standard equipment. All of the other NC-100 features
were retained, including the moving coil catacomb bandswitching, P-P
audio, tone control, noise limiter (1940 models and later) and an
optional crystal filter which was indicated by an "X" in the model
designation. During WWII, the Signal Corps wanted a somewhat
"militarized" version of the NC-100A. The receiver was designated as the
NC-100ASD. It had special frequency coverage that included a medium wave
band that tuned from 200kc up to 400kc. This required elimination of the
AM BC band coverage since there was only room in the coil catacomb for
five tuning ranges. The four higher frequency bands cover 1.2Mc to 30Mc.
A single audio tube was provided, a 6V6, as was the 500 Z ohm output
transformer that was to drive a matching loudspeaker that used an eight
inch diameter Jensen with 500Z to 2.8Z ohm matching transformer. The
loudspeaker cable was shielded to prevent RF pickup if the receiver was
operated near transmitters. The probable contract number for the
NC-100ASD is 9727-PHILA-43, dating from 1943. From reported serial
numbers, the highest of which is 948, it appears that around 1000
NC-100ASD receivers were built. Shown in the photo is NC-100ASD sn: 194
with its correct 500Z ohm matching loud speaker.

After the war, the
surplus market was certainly well-stocked with NC-100ASD receivers since
apparently the Signal Corps didn't find much use for these receivers.
Many ASDs were purchased surplus NOS at a price of $115 (1946 Newark
Electric price) complete with matching speaker and manual. During the
fifties and sixties, it was common to find the NC-100ASD used in many
novice and "teenage radio amateur" ham shacks where economics dictated
what sort of equipment was going to be in use. By then, ASDs were
certainly "second-hand" status and priced quite reasonably. Performance
was very good although QRM and lack of band spread probably limited most
successful operation to 80M and 40M (160M operation was problematic at
the time.)

There was also an
NC-100ASC version that was also designated as the AN/GRR-3. It appears
that this version is similar to a militarized NC-100XA.

The Navy also wanted
their own version of the NC-100A - it was designated as RAO - more
details above in Navy equipment.

ASP-1004
Receiver

Hammarlund Mfg. Co., Inc. - WWII Military Super-Pro 200 Series

The military had
several different Super-Pro versions built during WWII. Most versions
were nearly identical to their civilian counterparts in the SP-200 line.
As with most military contracts at that time, other companies besides
Hammarlund built the military Super-Pros (Howard Radio being the most
commonly seen.) The most popular military versions were BC-779(civilian
LX) covering 100 to 400kc and 2.5 to 20mc, BC-1004(civilian X) covering
.54 to 20mc and BC-794(civilian SX) covering 1.2 to 40mc. There were
other assigned model numbers also, probably depending on the end user of
the particular contract, e.g., the R-129/U that covered 300kc up to 10mc. Also, a suffix was sometimes added to the BC
designation indicating the type of power supply that went with each
receiver. Hammarlund's advertising implied that many Super-Pro receivers
were also used by our WWII Allies. Internally, there are only minor
changes made to the civilian Super-Pro for military use. Many of the
capacitors are combined into "bath-tub" type units that mount on the
side wall of the chassis. Also, the wiring harness uses stranded wire
and sometimes the solder joints are MFP'd. All of the WWII military
Super-Pros use a steel front panel that is copper plated under whatever
type of paint was used. Generally, the steel panels were painted with a
smooth finish and the stamped nomenclature was white filled. Panel
colors range from black or gray to shades of green-gray or blue-gray.
There were several variations in the construction of the power supply
also with most military versions using heavy-duty, over-size
transformers and chokes along with oil-filled filter condensers. Some
power supplies had dual primary or multiple tapped primary power
transformers to allow operation on 230/115vac or a variety of ac
voltages around 230/115vac. Designations are usually RA-74, RA-84 or
RA-94.

The military Super-Pro
receivers are great performers with fantastic audio, although most are
rack-mount versions which is a configuration not usually favored by
collectors. Additionally, many of the military models are in deplorable
condition today due their lack of appeal to hams during the last several
decades. The receivers not only require the normal electronic
restoration but a serious cosmetic restoration, too. Only recently has
the WWII Super Pro found an appreciative group of hams and collectors
that find the build quality and superior performance to be unmatched by
most of its contemporaries. Shown is a military ASP-1004 (same as
BC-1004) - probably destined for Allied use (ASP=Allied Super Pro?,)
with an original light greenish-gray panel, from the later part of WWII.
Note the eight holes around the outer edge of the panel - these are on
all military Super-Pro receivers and normally were there for
mounting the chassis dust cover. However, sometimes these receivers were
installed in a military desk-top cabinet designated CH-104-A with the
dust cover removed and screws and nuts installed in these holes. Russia
and Australia both built Super-Pro "knock-offs" during WWII, the KV-M
from Russia and the AMR-200 built by Eclipse Radio in Australia.

The Signal Corps
continued to support and use the SP-200 military versions post-WWI and
well into the 1950s with upgrades to the the receivers and additions to
the manual TM11-866. Improvement Kit MC-531 was a crystal oscillator kit
that could be installed and would provide improved frequency stability
with three selectable crystal controlled frequencies. There were other
uses post-WWII, such as the AN/FRR-12, that utilized two modified BC-794
receivers in dual diversity with crystal controlled oscillators and
crystal controlled BFO - all for reliable RTTY applications. The BC-794
receivers were professionally modified by Wickes Engineering and
Construction Company in 1948. The MC-531 concept went on to be improved
and incorporated into the standard design of the Hammarlund SP-600-JX
receiver, which was introduced in 1950.

See
"The Incredible Pre-War Super-Pro"
web article for more details on military Super-Pro receivers, navigation
link below.

the
Hallicrafters, Inc. - Army-Navy AN/GRR-2

Most of the SX-28 and SX-28A receivers built for the war
effort were standard Hallicrafters' production. In 1943, some SX-28s
were built to a "heavy-duty" configuration that included a potted power
transformer, dipped filter choke and audio output transformer and the
return to the gear-driven bandspread tuning. These "heavy-duty" SX-28
receivers went to the Navy and the Signal Corps. Around April 1944, the
SX-28A was introduced. It featured a series of improvements that had
been incorporated into the very last of the SX-28 production. The major
exception to these improvements was the High-Q Micro-set coils used in
the receiver's new front-end and the installation of these coils
warranted the designation change to "SX-28A." The U.S. Army Signal Corps
and the U.S. Navy, wanted the SX-28A in the special "heavy-duty" build
configuration and only these SX-28A receivers were given the
designation of AN/GRR-2. The GRR-2 receivers are quite different
from the standard SX-28A. The main differences are - the GRR-2 uses the
same potted power transformer built by General Transformer Company,
Korite dipped filter choke and audio output transformer and the
gear-driven bandspread tuning system. This gear-driven bandspread been
used in the earliest versions of the SX-28 receiver (the gear drive had
been replaced with a dial string drive in mid-1941 SX-28 production.)
The GRR-2 also has wax impregnated IF transformers and bandswitches, MFP
fungicide coating on the solder joints and special heavy duty nylon
insulated stranded hook-up wire in the harnesses. Additionally, the
GRR-2 front panel was copper plated under the dark gray paint and the
heavy-duty ball-end toggle switches have bakelite housings. The S-meter
is a special unit that uses a bakelite case and is mounted using a
special yoke system that mounts to the front panel with only two screws.
All GRR-2 receivers were originally configured as rack mounted
receivers and utilize a dust cover with hinged lid that provides ample
protection whether the receiver is actually rack mounted or used as a
table top receiver. The Signal Corps had its own manual for this
receiver - TM-11-874 - with more detailed information than the standard
SX-28A manual. The Signal Corps AN/GRR-2 shown is serial number HA-2703
and the fungicide dating is May 27, 1944. Only a few hundred AN/GRR-2
were produced.

National Co., Inc - HRO-W

The HRO-M was essentially a slightly updated version of
the HRO Senior that was introduced in 1941. The HRO-M was produced for
the military during most of WWII with many of the receivers being sent
to England. During HRO-M production, the lack of any identification for
the control function of the toggle switches that operated the B+ and the
AVC had been corrected by installing metal function "rings" around the
toggle switches. The HRO-M also replaced the "pull switch" used for the
S-meter with a toggle switch. Many HRO-M receivers were equipped with a
Marion Electric 0-1mA meter with a white scale that wasn't illuminated.
In 1945, the HRO-M was given a major upgrade that changed all of the
tubes to octal types with all tubes being the metal octal variety with
the exception of the 6V6GT audio output tube. Most of the components
under the chassis were changed to JAN types. Additionally, all of the
coil sets were given new aluminum silk-screened ID plates that were
mounted on the front panel of the coil set to provide a frequency chart
and a logging chart. National identified this receiver as the HRO-5.

The U.S. Army Signal Corps wanted a few subtle changes
and the HRO-5 model built for the Signal Corps was dubbed the HRO-W. The
minor changes were a data plate that specifies that the receiver is an
"HRO-W" along with extreme moisture and fungus proofing (MFP) of the
receiver. Most HRO-5 and HRO-W receivers will have the following
characteristics,...the S-meter will be a non-illuminated DC MA meter
with a white 0 to 1mA scale made by Marion Electric, the same company
that supplied the standard illuminated S-meter for the HRO receivers.
The "ball-handle" toggle switch used to disable the S-meter on the HRO-M
was replaced with a "bat-handle" toggle switch. Like most military HRO
receivers, the coil sets supplied were the "J" series versions for the
A, B, C and D coil sets. These were "general coverage" only - no
bandspread function on the JA, JB, JC or JD coils. The additional coil
sets that were supplied with the HRO-5/W were standard general coverage
and brought the total coils sets supplied to nine. The additional coil
sets were E, F, G, H and J sets which increased to coverage from 30mc
down to 50kc with a small section not covered (430kc to 480kc) around
the IF frequency (456kc.) The power supply was normally the Type 697
supply that had selectable primary voltages of 115vac or 230vac.
Typically, the military opt'd for an audio output transformer to remove
the B+ from the speaker terminals but the HRO-W doesn't follow this
pattern and the audio output transformer is mounted on the speaker, if
used. Generally, headsets were used for reception but this depended on
the installation and ultimate use of the receiver.

Note the receiver shown in the photo above,...not only
is the interior of the receiver given the MFP treatment but also the
knobs and switches. The MFP's yellow lacquer base gives the PW-D
micrometer dial a distinct "olive-drab" color and imparts the impression
that the knob skirts are brass. There is a silk-screen label under the
lid providing MFP treatment information which is date-stamped "JUL 29
1945."

BC-344-D Medium Wave Receiver - AC Operated

U.S.
Army Signal Corps - BC-312, BC-314, BC-342, BC-344 Series - Various
Contractors

The design of the BC-312, BC-314, BC-342 and the BC-344
receivers came from the U.S. Army Signal Corps in the late-thirties. Two
versions operated on +14vdc utilizing an internal dynamotor (the BC-312
and BC-314) while the other two versions (BC-342 and BC-344) operated on
120vac utilizing an internal power supply unit, the RA-20. All versions
of these receivers were stoutly built with rugged mechanical gear-driven
tuning, robust wiring technique and made use of a steel chassis with
extensive LO shielding utilizing a steel metal box. These receivers were
built to "take a beating" and still function. While the overall size of
the receivers is relatively small the weight is not - around 60 lbs -
mainly due to the "all steel" construction of each receiver. Some
aluminum is used (like the front panel) but the durability of the
receivers is aided by the steel cabinet and chassis. All alignment
adjustments have some kind of "tamper-proof" protection in the form of
locking nuts, protective shields or plug covers. The BC-312, 314, 342
and 344 series of receivers were used extensively in ground applications
from just before WWII up into the 1950s. The most common contractors
were Farnsworth Television & Radio Corp. for both AC and DC operated
receivers and RCA Manufacturing Co, Inc. for many of the early DC operated
receivers.

The circuit is a nine-tube superheterodyne (ten tubes in
the BC-342 and BC-344 which includes the 5W4 rectifier tube.) Two 6K7 RF
amplifiers are used along with a separate 6C5 Local Oscillator and 6L7
Mixer tube. Two 6K7 IF amplifiers, a 6C5 BFO, a 6R7 duplex-diode triode
for the Det/AVC/1st AF function and a 6F6 audio output tube complete the
tube line up. Frequency coverage is from 1500kc to 18000kc in six tuning
ranges for the BC-312 and BC-342. The BC-314 and BC-344 are medium wave
receivers and cover 150kc to 1500kc in four tuning ranges. The BC-312
and BC-314 are operated on 12-14vdc (BC-312-NX version 24-28vdc op) and
were intended for vehicular use, which could include trucks, cars, jeeps
or tanks. The BC-342 and BC-344 included the RA-20 AC power pack
allowing the receivers to operate on 110-120vac with the intended set-up
being a fixed station inside a building but mobile stations were
possible powered by a portable AC generator. The huge "trunk" connector
protruding out of the front panel allows power input on DC versions (or
filament voltage access on AC models,) telegraph key input, PTT and
microphone routing, remote stand-by (in DC versions,) audio outputs and
antenna relay function for interfacing with transmitters and other
equipment. All versions of the BC-342 have a Crystal Filter while the DC
operated versions will have a DIAL LIGHT control. Early versions of the
receivers will have a wire dial index and a fixed 4000Z ohm audio
output. All later versions have a plastic dial index and selectable
audio output impedance of either 250 ohms Z or 4K ohms Z. Some versions
allow access to the 1st AF output for earphone operation while the
typical BC-344 set-up has both phones and speaker outputs tied together
from the audio output transformer.

The receiver shown in the photo above is the BC-344-D
built by Farnsworth Television & Radio Corp. This is an AC operated,
medium wave receiver. Note that there isn't a Crystal Filter provided on
this version and, since it's AC operated, there is no DIAL LIGHT
control.

RESTORATION NOTES

Front Panel Removal:If you are planning to restore one of the BC-312/342 or
BC-314/344 receivers, be aware that the mechanical design does
not consider ease of maintenance beyond changing tubes
and routine alignment. Any of the receivers will be very
difficult to disassemble, requiring the unsoldering of several
connections and disassembly of other mechanical parts just to
remove the front panel.

Mechanically, the Fast Tuning gear and flanged shaft have to
be "un-pinned" so the gear and flanged shaft can be separated
and removed from the front panel and interior gear panel to
allow a front panel dismounting. Also, the front panel "trunk"
connector wires must all be unsoldered to dismount the front
panel and, additionally, there are some screws mounted to be
backside of the front panel that must be removed. Even the two
fuse holders must be unsoldered and removed before the front
panel can be dismounted. In all, any work involving front panel
removal is arduous.

The "phones" audio transformer is not accessible without
front panel removal and removal of the BFO assembly. Dismounting
any of the smaller assemblies is time consuming and usually
requires unsoldering joints where the wire was wrapped one and a
half turns before it was soldered. Additionally, there are many
different length screws and standoffs that have specific
locations so care must be observed during disassembly to keep
everything identified for proper reassembly. Front panel removal
is sure to result in several large piles of sorted screws and
other parts along with several drawings and notes before
reassembly can begin.

Shown in the photo above is the BC-312-N. This receiver has an
onboard dynamotor that operates on +14vdc to provide B+ to the
receiver. The tubes are standard 6 volt metal octals that are
wired in series-parallel. There is no Crystal Filter provided
but, since the BC-312 is DC operated, there is a DIAL LIGHT
control. The DC voltage input is via the front panel trunk
connector.

Other Problems:
Sometimes the OFF-MVC-AVC switch will have contact problems the
prevent the receiver from powering up. The switch is a
custom-built, stacked four level assembly that has no
replacement other than another original switch. It's easy to
access the power section of this switch since that section is
not enclosed. Rather, it is protected by a fiber board cover
that can easily be bent to access the contacts. Careful cleaning
and readjustment of the sliding arm and contact point can
usually get the switch working again. It seems that the contact
problems are more due to oxidation and dirt since these two
contacts are not sealed.

A common problem with later BC-312 et
al receivers is lack of transparency and warping of the plastic
dial index. Since the dial index assembly is mounted to the
backside of the front panel with eight screws that are
not accessible because of the dial assembly and mask, the front
panel must be dismounted to replace this problem-prone part. The
plastic is riveted to the metal bezel so removal of the deformed
original will require drilling out the rivets. Making a new
plastic dial index is fairly easy using thin plastic salvaged
from "cheap" picture frames. This material is flexible but has
some thickness to it and is fairly close to the original
material. Scribe an index line and fill the line with white
Artist's Acrylic paint, wiping off any excess so only the index
has paint in it. Mount the new plastic index by either using
rivets, fake rivets made from 2-56 screws and nuts or by
epoxy'ing the new piece in place. Note in the photo of the
BC-312 above that the dial index plastic has shrunk and warped
to the point where the dial mask nomenclature can be seen over
the .25" gap at the top of the dial cover. This is a "front
panel off" operation to replace this piece.

IMPORTANT
REASSEMBLY NOTES: When reinstalling the front panel
screws it will be noted that all of the 6-32 screws are the same
length but there are three different lengths of 4-40 screws.
There are two "short" 4-40 that must be installed in the correct
location otherwise the dial mask will be scratched when the band
switch is operated. One "short" 4-40 is installed near the band
switch knob and near the word "CHANGE" in the band switch
nomenclature. The other "short" 4-40 is installed near the
lower-left corner screw of the data plate. The four "long" 4-40
screws are for mounting the wire clamps that are made from fiber
blocks. The remaining 4-40 screws are all the same length.

On the AC operated models, the RA-20 power
supply uses a dual electrolytic filter capacitor. This is not
an oil-filled paper dielectric capacitor as used in other
military gear. The RA-20 filter capacitors are often bad and
require replacement. It's easy to use the original can to house
the modern replacement electrolytic capacitors. The RA-20 is
very compact and densely packed. There's no room for anything
other than the original parts. So, stuffing the replacement
electrolytics inside the original can is the good solution that
makes use of the available mounting bracket and hardware.

The photo right is a Farnsworth-built BC-342-N.
This is an early version of the "N" with the wire dial fiducial,
non-selectable audio output Z (fixed 4K ohms) and the typical
Signal Corps hand-written upgrade nomenclature above the ID tag.
Note that this version does have a Crystal Filter provided
(control is marked CRYSTAL PHASING.)

Final Notes:
Certainly the difficulty of performing any serious repair work
or modifications has "saved" many of the BC-312, '314, '342,
'344 receivers. Most of this family of receivers will be found
without extensive modifications. Many are found in "all
original" condition. Most receivers were heavily coated with MFP
and this also has prevented the "faint-of-heart" from performing
any serious rework to the receivers. Even the alignments are
usually close because all adjustments were "locked" with various
lock-nuts, plug covers or cover-shields. Quite different from
the BC-348 receivers that were easy to work on and thus are
always found with some modifications to originality. Sometimes
you might find a BC-312 that has the RA-20 installed but this is
easy to convert back to a stock, DC operated BC-312 as long as
you can find the correct dynamotor.

All of this laborious
restoration work will be rewarded as the BC-312/314/342/344
receivers are excellent performers with great sensitivity and
plenty of audio when driving a matched speaker. The stock LS-3
is a good match for the 4K impedance of
the BC-312 et al receivers.

Aircraft
Radio Equipment - USAAF

BC-224-H
- 1942

RCA
Manufacturing Company, Inc. - BC-224 Series and BC-348 Series -
Various Other Contractor Companies

RCA introduced the
BC-224 Aircraft Receiver in 1935. It ran on the then popular 12 volt
power systems used in most aircraft. The initial version of the BC-224
had the tuning dial on the left side of the front panel. This version is
usually designated as the BC-224-A and the number produced was very
small which was typical for pre-WWII military contracts. As aircraft
power systems improved 24 volts became the standard voltage and that
required a change in the radio equipment to be installed in the newer
airplanes. RCA redesigned the BC-224 to operate on 24 volts and this
receiver was designated as the BC-348. The BC-224 continued to be built
for installation into earlier aircraft while the BC-348 was produced for
modern aircraft installations. Both receivers were built by RCA
Manufacturing Co., Inc., a division of RCA that built all of the
commercial and military radio equipment for RCA (before WWII.) When WWII
began several other radio companies became contractors for BC-348
construction,... Belmont Radio, Wells-Gardner Co., Stromberg-Carlson, to
name a few. Only one contract for BC-224 receivers was built by another
company other than RCA Manufacturing Co., Inc. and the last contract for
the BC-224 appears in 1942. The BC-348 was produced through WWII and
total quantity produced is certainly well over 100,000 receivers (over
50,000 receivers alone were produced by Wells-Gardner Company.)

The BC-348 operates on
24-28vdc with the high voltage (~+220vdc) provided by an internal
dynamotor. Many thousands were built during WWII by many different
contractors building many different versions within that time period.
The circuit used eight tubes with the heaters originally wired in
dual-series for 24vdc operation (each of four 6 volt tube heaters in
series would operate on 24vdc.) The early circuit provided two RF
amplifiers, a Mixer, a Local Oscillator, an IF amplifier stage, a
combination 2nd IF amp and BFO, a combination 3rd IF amp and
Detector/AVC followed by a type 41 audio output stage (this was changed
to a 6K6 in some versions.) These versions will have a 991 neon lamp
acting as a regulator on the local oscillator and an antenna trim
control. Construction makes use of four component boards resulting in
extensive use of wiring harnesses. The Crystal Filter and BFO are in
fully shielded cans. This early version is usually referred to as the
"Grid Cap" version since these types of tubes are used. This early
version was difficult to work on and was expensive to build. To reduce
costs, the Q, N and J versions were introduced. These versions
eliminated most of the component boards and used "point to point" wiring
to reduce costs and ease rework. This version is called the
"Single-ended Tubes" version since "non-grid cap" tubes are used. The
later circuit used two RF amplifiers, a converter stage, three IF
amplifiers, a duplex diode/triode provided Detector, AVC and BFO
functions and a 6K6 provided the audio output. The later versions
eliminated the shielded Crystal Filter, Antenna Trim control and the
fully shielded BFO. The audio output impedance was internally selectable
at "low Z" which was around 300 Z ohms or "high Z" which was around 4000
Z ohms (on later versions.) Some BC-348s will have a decal on the front
panel indicating if the "low Z" was optioned. A selectable crystal
filter was also included in the circuit. The dual dial lamps were
adjustable for brightness and were wired in series through a
potentiometer and fixed resistor. Frequency coverage was from 200-500kc
(not on the B or C versions) and 1.5-18mc. The military considered the
two versions of the BC-348 to be interchangeable with virtually no
difference in performance and operation.

When the receiver was
installed on its FT-154 shock mount and installed in the
aircraft, an eight pin Jones plug mated with a receptacle and
cable that exited from the rear of the mount containing the
28vdc input, the remote stand-by relay function and an audio
output line. The BC-348 was generally interconnected with the
transmitter to control boxes allowing the transmitter's control
relay to provide antenna switching, receiver stand-by and
providing side tone monitoring which allowed for full "break-in"
keying. Since there are so many variations, military collectors
have generally divided the BC-348 into two groups, early types
(B, H, K, L, O, P & R) with grid cap type tubes ("Grid Capped
Tubes" version) and the later versions (J, N & Q) with
single-ended tubes ("Single-Ended Tubes" version.) Several of
the earlier versions were rebuilt into later configurations,
especially to add the 200-500kc band. Many different contractors
built BC-348s but Wells-Gardner Co. probably built the greatest
quantity of receivers and is the most commonly seen
manufacturer.

The
BC-348 became available as surplus almost immediately following
WWII and was easily available for several decades from many
surplus dealers. Many were available in the original box in the
late-forties. This allowed hams the ability to purchase a great
performing receiver at a reasonable price - NOS and still in the
crate for about $100. Many surplus dealer offered "AC power
supply conversions" for as little as $15, so the buyer didn't
have to do the work. The down side is that today it is almost
impossible to find a BC-348 that hasn't been modified.
Typically, the dynamotor was removed (and discarded) and an AC
power supply added. This mod was fairly simple and usually
didn't compromise the receiver's performance (other than adding
some hum to the audio output if the power supply wasn't
well-filtered - which most weren't.) Unfortunately, most of the
dealer power supply mods used a separate AC power toggle switch
that resulted in a non-original hole above the CW OSC. switch.

Many other
dubious mods were published in various surplus conversion books
from the fifties and sixties that did compromise the BC-348's
performance. Adding an S-meter or adding an audio output section
was common. Additionally, many hams would sometimes drill the
case with lots of .25" holes thinking the receiver needed extra
cooling because of the added AC power supply rectifier tube.
However, it's still possible to find unmolested examples and
many receivers just have the AC power supply added. These
examples usually aren't difficult to restore to original
condition. Both
versions the Grid Cap version and the Single-ended Tube versions are great performing receivers
if restored to original or when conservatively
modified (AC PS only.) Accurate alignment is also necessary for
top performance.

If you're interested in restoring your BC-348
or BC-224 receiver back to its original configuration with the
installation of the correct DM-28 or DM-24 dynamotor, go to our
web article "Rebuilding the BC-348 Family of Receivers" This
article tells you about all of the "pitfalls" that might await
you in this seemingly easy project. Also includes information on
other aspects of the restoration of these fine performing
receivers.

photo left: Wells-Gardner BC-348-Q 1943. This
contract produced over 40,000 receivers alone. Note that these
"Single Ended Tubes" versions eliminated the "ANT. ALIGN."
(antenna trimmer) control that was located above the Antenna and
Ground input terminals. Many other cost reductions will be found
inside the Q, N and J versions. However, the great performance
is retained and these receivers are very easy to do any rework
to.

General
Electric - BC-375-E

Though the BC-375 was designed in the early thirties and
utilized parts and technology from a decade earlier, it found a
long-term usage with the Signal Corps due to its ease of operation and
reliability. Its earlier kin, the BC-191, was the first version built
from the mid-thirties on up to mid-WWII. Around the beginning of WWII,
an airborne version was necessary and the BC-375 became the designation
for a slightly different transmitter for use in larger aircraft. GE got
a manufacturing contract for several tens-of-thousands of BC-375 that
were built through the first half of WWII. Commonly used on B-17s, the
SCR-287 set-up was found on thousands of those bombers. Hopelessly
outdated for aircraft use, towards the middle of WWII the ARC series of
transmitters-receivers were introduced, along with the Collins ART-13A,
to replace the BC-375. At the end of the war, thousands of BC-375-E
transmitters remained unopened in their original crates.

The BC-375 uses four VT-4-C triode tubes (type 211) and
a single VT-25 (10Y) triode with one VT-4 used as the Master Oscillator,
another VT-4 as the Power Amplifier and two VT-4 tubes for the P/P
Modulator. The VT-25 serves as the speech amplifier in the Voice mode
(AM,) as a 1000hz oscillator in the Tone mode (MCW) and as a sidetone
oscillator in the CW mode. Power is provided by the aircraft
battery/charger system (24 to 28vdc) and by a high voltage (+1000vdc)
dynamotor (PE-73.)

.

The transmitter frequency range is determined by which
of the seven Tuning Units is installed in the transmitter. The coils and
condensers and connections for the MO and PA are contained in each TU.
The range of frequencies is from 200kc to 500kc and from 1500kc up to
12500kc using the various TUs. The controls aligned vertically on the
right side of the transmitter make up the wide range antenna coupler for
the transmitter. The BC-306-A located to the right of the BC-375 is the
LF Antenna Tuner allowing further extension of antenna matching ability
below 800kc using the typical trailing wire antenna. Power output is
between 50 and 90 watts.

The BC-375 provides full break-in keying by allowing the
elaborate internal antenna relay to control the receiver antenna and the
receiver standby circuit. Additionally, external inputs via the PL-64
cable allow remote microphone and key operation along with remote power
control. The aircraft was usually set-up to allow the pilot to also
access the transmitter/receiver for various reasons.

After WWII, the BC-375 was available surplus for about
$15. The various TUs were also available at "give-away" prices. This
lead to many hams buying the BC-375 for an economical way to get "on
the air." Unfortunately, most hams tried to run the transmitter at full
power "as-is" or tried to rebuild it into something that it was
NEVER intended to be - a ham transmitter. The end result was a
bad reputation that the BC-375 was unstable, sounded awful, created
horrible TVI and was only useful as a resource for parts to build other
ham projects. Though TVI was a major issue in the fifties, today's
strong TV cable and satellite dish signals are usually not affected by
the BC-375 operation. The transmitter can sound fairly good if it is
carefully operated after a thorough check out that includes a precise
adjustment of the neutralization and reducing output power to about 50
watts.

For the ultimate information source on how to
successfully operate the BC-375 "on the air" without enduring endless
criticism of your signal's lack of audio quality, go to our web-article
"Successfully Operating the BC-375 on the Ham Bands Today" - navigation
link in the Index below.

SCR-287 - At the WHRM 2009 to 2012

The SCR-287 comprised a complete liaison radio station
installed onboard various bombers and transports during WWII. The
transmitter used was the BC-375 along with the BC-348 as a receiver. The
other components shown are the BC-348-Q receiver which does run on its
original dynamotor from the battery supply, the Lionel J-47 telegraph
key and the Shure Bros. carbon microphone, the T-17. The speaker is an
LS-3, although these were never used in the SCR-287 or onboard the
aircraft. Four BC-375 Tuning Units are mounted in their CS-48 containers
on the wall. The olive-drab console is not a WWII vintage item -
it's homebrew. It features a fold-down desk, a sound-proof (almost)
compartment for the PE-73 dynamotor and a bottom shelf for the four
storage batteries (four 12v batteries in series-parallel = 24vdc.) The
panel to the left of the BC-348 has all of the remote connections for
receiver audio output, receiver stand-by, xmtr CW sidetone select, xmtr
microphone input and xmtr key input. The photo shows the station as it
was set-up in the Western Historic Radio Museum in Virginia City, Nevada
from 2009 until 2012. The station is now set up in Dayton, Nevada where
it runs on a PP-1104 high current +28vdc power source (instead of +24vdc
worth the batteries.)

Setchell Carlson, Inc. - Model 524 Beacon Receiver

U.S.
Army Signal Corps Designation: BC-1206-CM

The Model 524 Beacon Receiver is a small size, light
weight aircraft receiver that covers 195kc up to 420kc. The circuit is a
five tube superheterodyne utilizing loctal type tubes. The receiver is
entirely powered by the +28vdc aircraft battery-charger buss. No higher
voltages are required to operate the 524. The "PHONES" output is 300
ohms Z although internally the output Z can be switched to 4000 ohms Z,
if desired. The IF is 135kc. The tubes used are RF Amp 14H7, Mixer 14J7,
IF Amp 14H7, Det-1st AF 14R7 and AF Output 28D7.

The 524 had a rather interesting use during WWII. These
small receivers were installed into the instrument panels of airplanes
that were going to flown to specific destinations by WASPs (Women's
Airforce Service Pilots.) This would generally be smaller fighter types
of aircraft but did include larger aircraft as well. The airplanes were
ferried from the manufacturer to either an airport or an export
facility. Since the destination was known, the 524 provided a way to
navigate to a specific airport via the beacon "beam." At that time,
airport beacon transmitters also provided weather reports and other
information necessary for piloting aircraft. Once the airplane was
delivered, the 524 was usually removed from the instrument panel and
returned to the aircraft factory where it was eventually recycled into
another aircraft destined for delivery.

The 524 is very sensitive with a specification of 3uv
for 10mw output. The receiver shown in the photo to the left does
function quite well and receives many NDBs and other signals in the
195kc to 420kc range. It is very small weighing only about 4 lbs and
measuring 4" x 4" x 6.625". The four holes in the front panel
surrounding the dial plate are tapped and are provided to allow mounting
the 524 into a standard instrument panel opening (3.125".)

the Hallicrafters, Inc. -
R-44/ARR-5

This VHF receiver
provided airborne search capabilities and was designed to find enemy
radar or other signals. The R-44 is a 14 tube superhet tuning from 27.8
to 143 Mc in three bands and receiving AM, CW or FM signals. Motor-drive
tuning provided a "search" scanning mode. Outputs for visual indicators
were also provided. A special "stub" antenna was used (AT-38) and a
separate power pack (PP-32) provided the power for the receiver (and
added three more tubes, although these were to provide B+ for three
individual receivers.) Sometimes this receiver is called the "Airborne
S-36" based on its similarity to Hallicrafters' VHF base receiver, the
S-36.

the
Hallicrafters, Inc. - R-45/ARR-7

Like the receiver above, the R-45 was an airborne search
and surveillance MF and HF (.55 to 43mc) receiver that was primarily
used for visual analysis of enemy radar and other types of signals. The
Panadaptor and Video Outputs were designed to feed into specific
airborne versions of typical panoramic adapters and to oscilloscopes.
The oscilloscopes sometimes had built-in oscillators to create lissajous
patterns for audio analysis of incoming signals (Video output is from
the 6V6 audio stage of the receiver.) The panoramic adapters monitored
the output of the Mixer stage of the receiver and provided a visual
representation of the spectrum surrounding the receiver's IF passband.
This allowed the operator to "see" signals that were outside the
receiver's passband and couldn't be heard - but they could be seen on
the panadapter, allowing the operator to tune to the signal for
investigation. The R-45's circuit is very similar to the SX-28A,
although "stripped down" to the essentials and considerably lightened
for aircraft use. 12 tubes are used (not including the rectifier that is
located in the PP-32 power pack.) Some of the similarities to the SX-28A
are the use of the same Micro-set coils in the front end, six
selectivity steps with three utilizing the crystal filter. The
differences from the SX-28A are the use of a "re-radiation" tube ahead
of the RF amps, a Noise Limiter which is just a clipper circuit, use of
a VR tube, no bandspread and the "militarily basic" audio output system
which is just a capacitive coupling from the 6V6 plate to drive the
headphones. Up to three combinations of the R-44 or the R-45 receivers
could be powered by the PP-32 power pack that provided the heater
voltage (6.3vac) and the B+ (+275vdc) but the scanning motor drive was
powered by the aircraft battery system (+24vdc.) Additionally, the PP-32
operated off of 115vac 400 cycle provided by the aircraft's ac system.

WWII Allied
Radio Equipment

Kingsley Radio Company, Melbourne, Australia - AR7

During WWII, both the Allies and the Axis copied the
famous National HRO Receiver. The Axis copies were shown in a 50th
Anniversary brochure that National published in 1964. Probably the
"knock-off" that got the most use was the Kingsley AR7, built during
WWII by Kingsley Radio Company of Melbourne, Australia. Kingsley
submitted the design (probably around 1940) as the K/CR/11 but after the
design was accepted, the receiver became the AR7. Though the AR7 uses a
micrometer dial and plug-in coil sets, that about as far as copying the
National HRO went. The AR7 did use two RF amplifiers but uses a
Converter stage instead of a separate LO and Mixer. Eight
"American-type" tubes are used in the receiver and two in the power
supply. Frequency coverage is 138kc up to 25mc using five plug-in coil
sets. Two IF amplifiers are also used operating at 455kc. An S-meter
amplifier circuit provides the user with a front panel Calibration
control. The audio output is a single 6V6 to a dual impedance output
transformer that provides 600 Z and 1750 Z impedances. A Crystal Filter
is provided. All AR7s are rack mounted and came with a rack mounted
power supply that operated on either 240vac or 12vdc. A rack mounted
speaker was also included. Some receiver housings had four coil storage
cubbies, two on each side of the receiver. Normally, the receiver was
lowest in the table rack with the speaker in the middle and the power
supply on top. The Australian Army referred to the AR7 as "Reception Set
No.1" and sometimes had the panels painted green. Normally, the AR7
panel, since it was a stainless steel overlay, was left unpainted with
the nomenclature slightly polished to improve readability.

After WWII, many AR7s were installed at various airports
around Australia where they served as tower and air to ground receivers.
Many were modified to have crystal controlled frequency reception with
the LO coils removed from the coil set and a crystal controlled fixed
frequency oscillator installed to allow specific frequency reception
with no tuning. Some receivers also had the AVC modified while others
had different scales installed on the S-meter. Most AR7s don't have the
original audio output transformer as it seems this component was easily
damaged. Banks of AR-7s could be found at various airport communications
facilities and some tower installations would feature a fairly stock AR7
that could still be tuned. Today, many AR7 receivers are in dismal
condition due to heavy use followed by indifferent storage. Most
receivers are incomplete and don't have the original power supply or
speaker panel. Many suffer from corrosion and are non-functional.

Performance of a functional AR7 is impressive. They are
similar to HROs but do have their quirks. For instance, the micrometer
dial tunes "backwards" when compared to the PW-D of the HRO. That is 500
on the AR-7 is the lowest frequency of the coil set installed while it's
the highest frequency with an HRO. Also, the S-meter works "backwards"
with FS being "0" and mechanical zero being "S-9." The ability to
calibrate the S-meter for the particular coil set being used is a nice
feature and not one that is found on the HRO. Coil sets are steel
construction and very heavy while the HRO sets are all aluminum. With
all of the use that the AR7 provided, both in WWII (and especially
post-WWII) it obviously was a great performer and very stable. The AR7
shown above is functional and doesn't have too many modifications to it.
Great audio, although it doesn't have the original audio output
transformer but rather has the commonly installed replacement
transformer made by Rola. Unfortunately, the Rola transformer only has a
single 600 Z ohm winding for the audio output.

Canadian Marconi Company - CSR-5

The Canadian Marconi Company was contracted to build a
high quality receiver for the Royal Canadian Navy in early 1943. Most
CSR-5 receivers were built in 1944 and were part of the first delivery
of receivers to the RCN. Sometime in 1944, the CSR-5A was introduced.
The CSR-5 was used for several purposes, even though its primary
intended use was aboard ship. Shipboard use required extensive shielding
in the receiver to allow its operation along side other equipment
without causing interference or radiating the LO from the antenna.
Apparently, the RCN found other uses for the CSR-5 and most were not
installed onboard ships until the early 1950s. The receiver's frequency
coverage was in two sections, 75kc to 530kc and 1.5mc to 30mc, in six
bands. Each scale on the large illuminated dial was color coded. The
CSR-5A replaced some of the 6SK7 tubes with 6SG7 tubes (in the RF and
IF) as the major change, however there were many other minor changes in
the cabinet style, power connector orientation, dial scales, etc. Many
of the earlier CSR-5 receivers were retrofitted with the 6SG7 tubes
which may cause confusion as to the receiver's original designation.
Additionally, the silk-screen was not changed for the chassis, so many
CSR-5A receivers will have modified 6SK7 to 6SG7 tube identification.

The CSR-5 has eleven tubes in the receiver with two RF
amplifiers, Mixer (also provides Xtal Osc function,) LO, two IF
amplifiers, NL, Det/1AF, AF output and Voltage Regulator. The RF Gain
control is a stepped attenuator type with about 10db of change for each
step. AF output is 2 watts into a 10K Z load for loudspeaker, 500 ohms Z
line audio and both Hi-Z and Lo-Z 'phones. A separate power supply is
required and the VP-3 provided 12vac Filament (series/parallel
connections for all 6.3vac tubes except the BFO and LO that use series
resistive loads) and +250vdc B+ with an input requirement of either
12vdc (vibrator PS) or 115/230vac. An AC only power supply was also
available and designated as the WE-11. Two 6X5 rectifiers are used in
the VP-3 bringing the receiver's total tube count to 13 tubes. The later
version CSR-5A was mostly built after the initial contract of CSR-5
receivers although it could be possible that the production overlapped.
CSR-5A receivers were built up into 1945. The receivers were used
actively through most of the 1950s.

The CSR-5 and 5A are found in a variety of different
paint colors with the most common color found being a smooth finish,
light cream color with a slight greenish tint. Smooth gray is also found
when the receiver was part of a rack system. Gray wrinkle finish is
common in the stand-alone receivers. Different shades of gray are often
encountered along with black wrinkle finish. Many different shade and
texture variations will be found along with both black or white
nomenclature. Some paint combinations are original but most of the
unusual variations are from military repaint jobs. The CSR-5 shown in
the photo above has the name plate mounted on the front panel. This is
not standard as most receivers have the name plate mounted on the
top lid of the cabinet. Only the CSR-5A will have the "Marconi"
script along with "CANADA CSR-5A"
silk-screened on the center area of the escutcheon. The CSR-5 is a good
performer with all of the characteristics (both good and bad) found in
mid-forties military receivers. Due to the VR tube and filament loads on
the LO and BFO tubes, the CSR-5 exhibits very little drift after a short
warm-up. Sensitivity is competitive with mid-1940s designs and although
a crystal filter is included it doesn't have a front panel phasing
control.

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